ci: Add workflow running vimscript linter

Author: alerque

.github/workflows/vint.yml

@@ -0,0 +1,15 @@
+name: Vint
+on: [push]
+jobs:
+  vint:
+    name: vint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up Python
+        uses: actions/setup-python@v2
+      - name: Setup dependencies
+        run: pip install vim-vint
+      - name: Lint Vimscript
+        run: vint .

README.markdown

@@ -1,5 +1,7 @@
 # Indent Guides
 
+[![Vint](https://github.com/preservim/vim-indent-guides/workflows/Vint/badge.svg)](https://github.com/preservim/vim-indent-guides/actions?workflow=Vint)
+
 Indent Guides is a plugin for visually displaying indent levels in Vim.
 
 <img src="http://i.imgur.com/ONgoj.png" width="448" height="448" alt="" />