Update README.md

Adding PostgreSQL to README as an alternative requirement
Issue 3941: Code preview dark doesn't display correctly with long lines

Assigning the background color to the pre tag did not work correctly. Moved background color to the highlight class which fixes the problem.
Add background color to pre, too.
Merge pull request #3942 from bke-drewb/issue3941

Issue 3941: Code preview dark doesn't display correctly with long lines
Merge pull request #3940 from frlan/patch-3

Update README.md
better wording encouraging usage of latest stable release in GitLab Maintenance Policy
A little change on wording for new-user email

adds missing wording missed in https://github.com/gitlabhq/gitlabhq/commit/58d6176bc35fb45427df75b9762df6bb0d3b3a98 and https://github.com/gitlabhq/gitlabhq/pull/3902
Dont parse gfm-extractions as commit. Increase gfm rendering speed. Especially for a lot of code snippets
Merge pull request #3909 from bbodenmiller/patch-5

better wording encouraging usage of latest stable release in GitLab Maintenance Policy
Merge pull request #3961 from bbodenmiller/patch-1

A little change on wording for new-user email
add deploy recipe extracted from staging server
Fix skipping of some elements in makrdown
Added spec on bulk issues update
Cleanup bulk issues update a bit
Added few tests on Issues::BulkUpdateContext
minor styling for dark themes
respect whitespaces in blame view
Merge pull request #3956 from AlexDenisov/issues_bulk_update

Issues bulk update
Its time for 5.2.0.rc1
Fix typo in install docs, closes #3723