Regression in README selection for project page

Related to https://gitlab.com/gitlab-com/support-forum/issues/511

Introduced in 6ce01ca3

Previously, we selected the first previewable README file in a repository. In the case of README and README.md being present, we preferred README.md. After the above commit, we now prefer README. Maybe this change is intentional, but it did change the behavior. Once example repository is https://gitlab.com/cryptsetup/cryptsetup which has both files. README.md one is the one the user wants to have displayed and was displayed before 8.4 RC's.

cc/ @dbalexandre

mentioned in issue #7961 (closed)

mentioned in issue gitlab-com/support-forum#511 (closed)

@dblessing I think we can change to the old behavior to prefere README.md instead of README if both exists in the repository. Wdyt?

Reassigned to @dbalexandre

@dbalexandre I think we should prioritize Markdown over plaintext.

Milestone changed to 8.4

@rspeicher Thanks! I'm working on it right now :)

mentioned in issue cryptsetup/cryptsetup#278 (closed)

mentioned in merge request !2521 (merged)

Status changed to closed by commit 991cd076

mentioned in commit 991cd076