Update outdated translation instructions in How to Help
As noted by nykula in the comments on https://hosted.weblate.org/translate/f-droid/website-docs/en/?checksum=b09ee18292852e2a#comments.
As noted by nykula in the comments on https://hosted.weblate.org/translate/f-droid/website-docs/en/?checksum=b09ee18292852e2a#comments.