Mention our policy on typofixes for internal docs and tests

Author: apiraino

src/how-to-start-contributing.md

@@ -110,15 +110,23 @@ There are various ways in which you can contribute to Rust projects:
   you can help improve our GitHub CI workflows, automation Python scripts or contribute to web
   frontends with HTML/CSS/JS (e.g. [Rustdoc][rustdoc-ui] or [Benchmark suite website][rustc-perf-ui]).
   Play to your strengths!
+
 - Improving documentation is possibly one of the easiest starting points for contributions.
   Did you find a typo, something that was unclear, or do you miss some useful information on this
   page, elsewhere in the Forge or in some other Rust (user-facing) documentation? Great, then send
   a pull request and you'll become a contributor! :)
+
+  Please notice that at this time **we don't accept typography/spellcheck fixes to internal documentation or in our
+  testsuite** (reason: they could inadvertedly cause code regressions)
+
 - Improving tests is also very valuable, as there is never enough of them. This can include also
   documenting existing tests or writing tests for already fixed issues that lack a proper test.
+
 - You can also help with improving issue trackers of our repositories, by helping with [triaging issues][issue-triage]
   or by reproducing old issues to find out whether they are still valid or not.
+
 - Or, if you like programming language discussions, you could participate in our [RFC process](https://github.com/rust-lang/rfcs).
+
 - You can also answer questions to help other Rust users, in the _Get Help!_ channels on the [Rust Discord
   server][rust-discord], on [users.rust-lang.org][users] (URLO), or on [StackOverflow][so].