Merge branch 'doc_release_channels' into rollup

diff --cc src/doc/trpl/SUMMARY.md
index 03350de4af530a61e5d275b427ebb0a65e4d26a4,fef61dcc70229b0b41750d44c91ae8972627e060..f3a3fd635e43ebfc28237c97bfe179b03f3b493e
--- 1/src/doc/trpl/SUMMARY.md
--- 2/src/doc/trpl/SUMMARY.md
+++ b/src/doc/trpl/SUMMARY.md
@@@ -16,7 -15,7 +16,8 @@@
      * [Concurrency](concurrency.md)
      * [Error Handling](error-handling.md)
      * [FFI](ffi.md)
 +    * [Borrow and AsRef](borrow-and-asref.md)
+     * [Release Channels](release-channels.md)
  * [Syntax and Semantics](syntax-and-semantics.md)
      * [Variable Bindings](variable-bindings.md)
      * [Functions](functions.md)