chore: add cabal.project.local to .gitignore

Author: ncfavier

.gitignore

@@ -14,7 +14,7 @@ wip/
 .ghci
 hie.yaml
 /*.sh
-cabal.project
+cabal.project.*
 
 # Build output
 /html

cabal.project

@@ -2,6 +2,9 @@ packages: support/shake/1lab-shake.cabal
 
 -- To build outside of the Nix shell, uncomment the following stanza
 -- and replace `master` with the `rev` field from `support/nix/dep/Agda/github.json`.
+--
+-- If you want to avoid polluting your Git tree, you can move this to
+-- `cabal.project.local`, which is ignored by Git.
 
 -- source-repository-package
 --   type: git