[add] github actions

[add] github actions's batch in README

[update] yml

.github/ISSUE_TEMPLATE.md

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+#### environment
+
+- vim: ????
+- vim-airline: ????
+- OS: ????
+- Have you reproduced with a minimal vimrc: ???
+- What is your airline configuration: ???
+if you are using terminal:
+- terminal: ????
+- $TERM variable: ???
+- color configuration (:set t_Co?):
+if you are using Neovim:
+- does it happen in Vim: ???
+
+#### actual behavior
+
+????
+
+#### expected behavior
+
+????
+
+#### screen shot (if possible)

.github/workflows/reviewdog.yml

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+name: reviewdog
+on: [push, pull_request]
+jobs:
+  vint:
+    name: runner / vint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: vint
+        uses: reviewdog/action-vint@v1
+        with:
+          github_token: ${{ secrets.github_token }}
+          reporter: github-pr-review