Auto merge of #40765 - pirate:patch-3, r=aturon

Add contribution instructions to stdlib docs

Generally programming language docs have instructions on how to contribute changes.

I couldn't find any in the rust docs, so I figured I'd add an instructions section, let me know if this belongs somewhere else!

src/libstd/lib.rs

@@ -94,6 +94,17 @@
 //! compiler - but they are documented here the same). Like the prelude, the
 //! standard macros are imported by default into all crates.
 //!
+//! # Contributing changes to the documentation
+//!
+//! Check out the rust contribution guidelines [here](
+//! https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md).
+//! The source for this documentation can be found on [Github](https://github.com/rust-lang).
+//! To contribute changes, make sure you read the guidelines first, then submit
+//! pull-requests for your suggested changes.
+//!
+//! Contributions are appreciated! If you see a part of the docs that can be
+//! improved, submit a PR, or chat with us first on irc.mozilla.org #rust-docs.
+//!
 //! # A Tour of The Rust Standard Library
 //!
 //! The rest of this crate documentation is dedicated to pointing out notable