+If you run `./x.py build` now, and you are lucky, it may just work. If you see
+an error message about patches that did not resolve to any crates, you will need
+to complete a few more steps which are outlined with their rationale below.
+
+*(This error may change in the future to include more information.)*
+```
+error: failed to resolve patches for `https://github.com/rust-lang/rustfmt`
+
+Caused by:
+ patch for `rustfmt-nightly` in `https://github.com/rust-lang/rustfmt` did not resolve to any crates
+failed to run: ~/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo build --manifest-path ~/rust/src/bootstrap/Cargo.toml
+```
+
+If you haven't used the `[patch]`
+section of `Cargo.toml` before, there is [some relevant documentation about it
+in the cargo docs](http://doc.crates.io/manifest.html#the-patch-section). In
+addition to that, you should read the
+[Overriding dependencies](http://doc.crates.io/specifying-dependencies.html#overriding-dependencies)
+section of the documentation as well.
+
+Specifically, the following [section in Overriding dependencies](http://doc.crates.io/specifying-dependencies.html#testing-a-bugfix) reveals what the problem is:
+
+> Next up we need to ensure that our lock file is updated to use this new version of uuid so our project uses the locally checked out copy instead of one from crates.io. The way [patch] works is that it'll load the dependency at ../path/to/uuid and then whenever crates.io is queried for versions of uuid it'll also return the local version.
+>
+> This means that the version number of the local checkout is significant and will affect whether the patch is used. Our manifest declared uuid = "1.0" which means we'll only resolve to >= 1.0.0, < 2.0.0, and Cargo's greedy resolution algorithm also means that we'll resolve to the maximum version within that range. Typically this doesn't matter as the version of the git repository will already be greater or match the maximum version published on crates.io, but it's important to keep this in mind!
+
+This says that when we updated the submodule, the version number in our
+`src/tools/rustfmt/Cargo.toml` changed. The new version is different from
+the version in `Cargo.lock`, so the build can no longer continue.
+
+To resolve this, we need to update `Cargo.lock`. Luckily, cargo provides a
+command to do this easily.
+
+```
+$ cargo update -p rustfmt-nightly
+```
+
+This should change the version listed in `Cargo.lock` to the new version you updated
+the submodule to. Running `./x.py build` should work now.
+
+## Writing Documentation
+
+Documentation improvements are very welcome. The source of `doc.rust-lang.org`
+is located in `src/doc` in the tree, and standard API documentation is generated
+from the source code itself. Documentation pull requests function in the same way
+as other pull requests.
+
+To find documentation-related issues, sort by the [T-doc label][tdoc].
+
+[tdoc]: https://github.com/rust-lang/rust/issues?q=is%3Aopen%20is%3Aissue%20label%3AT-doc
+
+You can find documentation style guidelines in [RFC 1574][rfc1574].
+
+[rfc1574]: https://github.com/rust-lang/rfcs/blob/master/text/1574-more-api-documentation-conventions.md#appendix-a-full-conventions-text
+
+In many cases, you don't need a full `./x.py doc`. You can use `rustdoc` directly
+to check small fixes. For example, `rustdoc src/doc/reference.md` will render
+reference to `doc/reference.html`. The CSS might be messed up, but you can
+verify that the HTML is right.
+
+Additionally, contributions to the [rustc-dev-guide] are always welcome. Contributions
+can be made directly at [the
+rust-lang/rustc-dev-guide](https://github.com/rust-lang/rustc-dev-guide) repo. The issue
+tracker in that repo is also a great way to find things that need doing. There
+are issues for beginners and advanced compiler devs alike!
+
+## Issue Triage
+
+Sometimes, an issue will stay open, even though the bug has been fixed. And
+sometimes, the original bug may go stale because something has changed in the
+meantime.
+
+It can be helpful to go through older bug reports and make sure that they are
+still valid. Load up an older issue, double check that it's still true, and
+leave a comment letting us know if it is or is not. The [least recently
+updated sort][lru] is good for finding issues like this.
+
+Contributors with sufficient permissions on the Rust repo can help by adding
+labels to triage issues:
+
+* Yellow, **A**-prefixed labels state which **area** of the project an issue
+ relates to.
+
+* Magenta, **B**-prefixed labels identify bugs which are **blockers**.
+
+* Dark blue, **beta-** labels track changes which need to be backported into
+ the beta branches.
+
+* Light purple, **C**-prefixed labels represent the **category** of an issue.
+
+* Green, **E**-prefixed labels explain the level of **experience** necessary
+ to fix the issue.
+
+* The dark blue **final-comment-period** label marks bugs that are using the
+ RFC signoff functionality of [rfcbot] and are currently in the final
+ comment period.
+
+* Red, **I**-prefixed labels indicate the **importance** of the issue. The
+ [I-nominated][inom] label indicates that an issue has been nominated for
+ prioritizing at the next triage meeting.
+
+* The purple **metabug** label marks lists of bugs collected by other
+ categories.
+
+* Purple gray, **O**-prefixed labels are the **operating system** or platform
+ that this issue is specific to.
+
+* Orange, **P**-prefixed labels indicate a bug's **priority**. These labels
+ are only assigned during triage meetings, and replace the [I-nominated][inom]
+ label.
+
+* The gray **proposed-final-comment-period** label marks bugs that are using
+ the RFC signoff functionality of [rfcbot] and are currently awaiting
+ signoff of all team members in order to enter the final comment period.
+
+* Pink, **regression**-prefixed labels track regressions from stable to the
+ release channels.