bevy-website repo: Setup instructions including linters/formatters which should be used.

Its possible to figure some of the linters/tools that are used by looking at the various dot-files in this repo, but it would be very useful to have that mentioned in the readme or contributing/developing guide.

Case in point: I only noticed mega-linter after one of my PRs failed CI.

Inspect the repository's dot-files and CI configuration to identify the linters and formatters currently used, including mega-linter. Update the README or contributing/developing guide with those setup instructions; done means contributors can find the required tools without discovering them through a failed CI run.

Written by the indexing model from the issue text.