Add pre-commit setup to the Lifecycle of a pull request

[nineteendo]

Describe the enhancement or feature you'd like

Currently we don't mention pre-commit anywhere in the dev guide. If we explain how to set it up, this could save unnecessary CI churn.

• PR: Add pre-commit setup to the Lifecycle of a pull request #1306

[erlend-aasland]

Would you like to propose a PR to the devguide?

[nineteendo]

I'll see what I can do.