Add Pull Request Labeler

Adds an automated pull request labeler to allow for better organization of workflow. This automated labeler uses [GitHub Actions](https://github.com/features/actions) and runs every time a pull request is made to the repo.

This requires issue #475 to be implemented in order to work seamlessly.

Author: soumitradev

.github/labeler.yml

@@ -0,0 +1,12 @@
+docs:
+  - "docs/**/*"
+
+CI:
+  - "**/*.yml"
+  - ".github/workflows/**/*"
+
+testing:
+  - "test/*"
+  
+source:
+  - "src/**/*"