refactor(users/glittershark): Rename to grfn

Rename my //users directory and all places that refer to glittershark to
grfn, including nix references and documentation.

This may require some extra attention inside of gerrit's database after
it lands to allow me to actually push things.

Change-Id: I4728b7ec2c60024392c1c1fa6e0d4a59b3e266fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2933
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/grfn/xanthous/README.org

@@ -0,0 +1,36 @@
+#+TITLE: Xanthous
+
+* Building
+
+#+BEGIN_SRC shell
+$ nix build
+#+END_SRC
+
+* Running
+
+#+BEGIN_SRC shell
+$ ./result/bin/xanthous [--help]
+#+END_SRC
+
+** Keyboard commands
+
+Keyboard commands are currently undocumented, but can be found in [[[https://github.com/glittershark/xanthous/blob/master/src/Xanthous/Command.hs#L26][this file]].
+Movement uses the nethack-esque hjklybnu.
+
+* Development
+
+Use [[https://github.com/target/lorri][lorri]], or run everything in a ~nix-shell~
+
+#+BEGIN_SRC shell
+# Build (for dev)
+$ cabal new-build
+
+# Run the game
+$ cabal new-run xanthous
+
+# Run tests
+$ cabal new-run test
+
+# Run a repl
+$ cabal new-repl
+#+END_SRC