[workflows.md] Add guidelines on how to write CL descriptions
[workflows.md] Add guidelines on how to write CL descriptions

This adds a guideline to our documentation on how to write
and format CL descriptions.

Also-by: 246a7797c718d5c57d87b3a8c56742f1c3829cb8@google.com
Bug: none
Change-Id: I354f5c4b42ee4c3c711d29e7bbf3884cc2ea29fb
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3687724
Reviewed-by: Jecelyn Yeen <f9d8706cc517861f2adda0a78fda4fb3953b5665@chromium.org>
Commit-Queue: Kim-Anh Tran <a72f38a79b5fac6811022b8a7fb84830d856c9c9@chromium.org>

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