Fewer links means less confusion.
- Merge doom-issue and doom-commit links into doom-ref (for auto-linking
Issue/PR/commit references).
- Merge doom-module-source and doom-docs-source links into doom-source.
- Rename doom-report-issue to doom-report.
- Use '!' as the icon for module issues link.
- Remove doom-repo (replaced with "doom:*" in :lang org module).
- Add doomdir and emacsdir links to :lang org module.
These instructions were tested on openSUSE Tumbleweed and openSUSE Leap
15.1. There are some modules left that are not documented yet, but this
already improves the sitution for common openSUSE users.
