[3.4] More aggressively point people at Rust version docs (#5782)

docs/faq.rst

@@ -123,7 +123,9 @@ Installing ``cryptography`` fails with ``error: Can not find Rust compiler``
 Building ``cryptography`` from source requires you have :ref:`Rust installed
 and available<installation:Rust>` on your ``PATH``. You may be able to fix this
 by upgrading to a newer version of ``pip`` which will install a pre-compiled
-``cryptography`` wheel. If not, you'll need to install Rust.
+``cryptography`` wheel. If not, you'll need to install Rust. Follow the
+:ref:`instructions<installation:Rust>` to ensure you install a recent Rust
+version.
 
 For the current release *only* you can temporarily bypass the requirement to
 have Rust installed by setting the ``CRYPTOGRAPHY_DONT_BUILD_RUST`` environment

docs/installation.rst

@@ -273,6 +273,8 @@ Building ``cryptography`` requires having a working Rust toolchain. The current
 minimum supported Rust version is 1.45.0.
 
 Instructions for installing Rust can be found on `the Rust Project's website`_.
+We recommend installing Rust with ``rustup`` (as documented by the Rust
+Project) in order to ensure you have a recent version.
 
 .. _`Homebrew`: https://brew.sh
 .. _`MacPorts`: https://www.macports.org

setup.py

@@ -169,7 +169,10 @@
        instructions for your platform.
     3) Check our frequently asked questions for more information:
        https://cryptography.io/en/latest/faq.html
-    4) Ensure you have a recent Rust toolchain installed.
+    4) Ensure you have a recent Rust toolchain installed:
+       https://cryptography.io/en/latest/installation.html#rust
+    5) If you are experiencing issues with Rust for *this release only* you may
+       set the environment variable `CRYPTOGRAPHY_DONT_BUILD_RUST=1`.
     =============================DEBUG ASSISTANCE=============================
     """
     )