Merge branch 'mchrastek-translation-validation-doc' into 'master'

Add info about posting validation issues to Crowdin to translation docs

Closes gitlab-com/localization/localization-team#245

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/168361



Merged-by: Ashraf Khamis <akhamis@gitlab.com>
Co-authored-by: Martin Chrástek <mchrastek-ext@gitlab.com>