readme: Clarify clang-format usage/version

README.md

@@ -241,8 +241,11 @@ scripts/format-project.sh
 
 You can optionally put something like `CLANG_FORMAT=clang-format-7` before that command
 if your clang-format binary isn't named `clang-format`.
-Note that you'll typically prefer to use something like `git clang-format`
+**Note that you'll typically prefer** to use something like `git clang-format`
 to just re-format your changes, in case version differences in tools result in overall format changes.
+The CI "style" job currently runs on Debian Buster, so it has clang-format-7.
+We will probably update that job to Bullseye or Ubuntu 20.10, which will allow
+using clang-format-11 by default, soon.
 
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