Gitpod: clarify pre-commit error message

[reshamas]

The error message displayed by VS Code when pre-commit fails can be confusing.

It may be worthwhile documenting that in a subsequent PR.

Originally posted by @maresb in #6549 (comment)

[maresb]

[I trimmed out the previous comment about fixing the pre-commit hook which isn't directly related to documenting the confusing pre-commit error message.]

To reproduce, attempt to commit a superfluous change, like one that adds extra newlines in an arbitrary .py file. Then you'll get a message about Git failing, but the pre-commit message is not directly displayed until you push the right button..