Add auto-lock workflow

.github/workflows/lock.yml

@@ -0,0 +1,17 @@
+name: 'Lock threads'
+
+on:
+  schedule:
+    - cron: '0 0 * * *'
+
+jobs:
+  lock:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v2
+        with:
+          github-token: ${{ github.token }}
+          issue-lock-inactive-days: '30'
+          issue-lock-reason: ''
+          pr-lock-inactive-days: '30'
+          pr-lock-reason: ''

README.md

@@ -7,7 +7,7 @@
 <a href="https://circleci.com/gh/jarun/workflows/buku"><img src="https://img.shields.io/circleci/project/github/jarun/buku.svg" alt="Build Status" /></a>
 <a href="http://buku.readthedocs.io/en/latest/?badge=latest"><img src="https://readthedocs.org/projects/buku/badge/?version=latest" alt="Docs Status" /></a>
 <a href="https://en.wikipedia.org/wiki/Privacy-invasive_software"><img src="https://img.shields.io/badge/privacy-✓-crimson" alt="Privacy Awareness" /></a>
-<a href="https://github.com/jarun/buku/blob/master/LICENSE"><img src="https://img.shields.io/badge/license-GPLv3-yellow.svg?maxAge=2592000" alt="License" /></a>
+<a href="https://github.com/jarun/buku/blob/master/LICENSE"><img src="https://img.shields.io/badge/license-GPLv3-yellowgreen.svg?maxAge=2592000" alt="License" /></a>
 </p>
 
 <p align="center">