doc/rusticl: add Rust Update Policy

Signed-off-by: Karol Herbst <git@karolherbst.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23110>

docs/rusticl.rst

@@ -33,6 +33,29 @@ the occasional use of enums, structs or constants through the code base.
 If you need help ping ``karolherbst`` either in ``#dri-devel`` or
 ``#rusticl`` on OFTC.
 
+Rust Update Policy
+------------------
+
+Given that for some distributions it's not feasible to keep up with the
+pace of Rust, we promise to only bump the minimum required Rust version
+following those rules:
+
+-  Only up to the Rust requirement of other major Linux desktop
+   components, e.g.:
+
+   -  `Firefox ESR <https://whattrainisitnow.com/release/?version=esr>`__:
+      `Minimum Supported Rust Version:
+      <https://firefox-source-docs.mozilla.org/writing-rust-code/update-policy.html#schedule>`__
+
+   -  latest `Linux Kernel Rust requirement
+      <https://docs.kernel.org/process/changes.html#current-minimal-requirements>`__
+
+-  Only require a newer Rust version than stated by other rules if and only
+   if it's required to get around a bug inside rustc.
+
+As bug fixes might run into rustc compiler bugs, a rust version bump _can_
+happen on a stable branch as well.
+
 Contributing 
 ------------