Add custom Cows and Figlet directories to .gitignore

Summary: These directories didn't get added to `.gitignore`, but should be.

Test Plan:
  - Touched a dummy file in each directory.
  - Ran `git status`.
  - Didn't see the file show up.

Reviewers: chad, cspeckmim

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D14249

.gitignore

@@ -34,3 +34,7 @@
 
 # NPM local packages
 /support/aphlict/server/node_modules/
+
+# Places for users to add custom resources.
+/resources/cows/custom/*
+/resources/figlet/custom/*