Doc for update from 5.3 to 5.4
Update installation.md

fixed branch-name (5-3 -> 5-4)
Merge pull request #4589 from lukas2511/patch-1

Update installation.md
Merge branch '5-4-stable' of github.com:mongris/gitlabhq into 5-4-stable

* '5-4-stable' of github.com:mongris/gitlabhq:
  Update installation.md
  Doc for update from 5.3 to 5.4
Support table and toc in markdown