ci: Add some descriptions of the stages

.gitlab-ci.yml

@@ -12,12 +12,12 @@ before_script:
   - "git fetch https://gitlab.haskell.org/ghc/ghc-performance-notes.git refs/notes/perf:refs/notes/perf || true"
 
 stages:
-  - lint
-  - build
-  - full-build
-  - cleanup # See Note [Cleanup on Windows]
-  - packaging
-  - hackage
+  - lint       # Source linting
+  - build      # A quick smoke-test to weed out broken commits
+  - full-build # Build all the things
+  - cleanup    # See Note [Cleanup on Windows]
+  - packaging  # Source distribution, etc.
+  - hackage    # head.hackage testing
 
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 # Runner Tags