Add Labeler Actions (#1074)

* adds labels to PRs

this will label PRs such that 
the maintainers have visibility into 
the breadth of the changes being suggested

* Create labeler.yml

* add all shell completions to labeler

any changes to and autocomplete for any shell
will now be auto labelled as impacting the autocompletion functionality

.github/labeler.yml

@@ -0,0 +1,12 @@
+# changes to documentation
+"area/documentation": doc/**/*
+
+# changes to the core lib package
+"area/lib": ./*.go
+
+# changes to the zsh completion
+"area/*sh completion":
+  - ./zsh_*
+  - ./shell_*
+  - ./powershell_*
+  - ./bash_*

.github/workflows/label.yml

@@ -0,0 +1,19 @@
+# This workflow will triage pull requests and apply a label based on the
+# paths that are modified in the pull request.
+#
+# To use this workflow, you will need to set up a .github/labeler.yml
+# file with configuration.  For more information, see:
+# https://github.com/actions/labeler/blob/master/README.md
+
+name: Labeler
+on: [pull_request]
+
+jobs:
+  label:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/labeler@v2
+      with:
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"