Add clause to etiquette about using English

Author: apiraino

src/how-to-start-contributing.md

@@ -128,6 +128,7 @@ To achieve this goal, we want to build trust and respect of each other's time an
 - If you want to fix an issue but have doubts about the design, you're welcome to join our [Zulip][rust-zulip] server and ask for tips
 - Please respect the reviewers' time: allow some days between reviews, only ask for reviews when your code compiles and tests pass, or give an explanation for why you are asking for a review at that stage (you can keep them in draft state until they're ready for review)
 - Try to keep comments concise, don't worry about a perfect written communication. Strive for clarity and being to the point
+- We prefer using the English language to follow conventions of existing commits. Again, don't worry about writing a perfect prose
 
 [^1]: Free-Open Source Project, see: https://en.wikipedia.org/wiki/Free_and_open-source_software