Add vimscript linter as CI check

.github/workflows/vint.yml

@@ -0,0 +1,18 @@
+name: Vint
+on: [push, pull_request]
+jobs:
+  vint:
+    strategy:
+      fail-fast: false
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@master
+    - name: Set up Python
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Setup dependencies
+      run: pip install vim-vint
+    - name: Run Vimscript Linter
+      run: vint .

README.md

@@ -1,4 +1,4 @@
-# NERD Commenter
+# NERD Commenter [![Vint](https://github.com/preservim/nerdcommenter/workflows/Vint/badge.svg)](https://github.com/preservim/nerdcommenter/actions?workflow=Vint)
 
 Comment functions so powerful—no comment necessary.