Add github action and update README

Author: quiqueporta

.github/workflows/tests.yml

@@ -0,0 +1,31 @@
+name: Tests
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        lua-version: ["5.1", "5.2", "5.3", "5.4"]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Lua
+        uses: leafo/gh-actions-lua@v10
+        with:
+          luaVersion: ${{ matrix.lua-version }}
+
+      - name: Setup LuaRocks
+        uses: leafo/gh-actions-luarocks@v4
+
+      - name: Install dependencies
+        run: luarocks install busted
+
+      - name: Run tests
+        run: busted

README.md

@@ -1,5 +1,9 @@
 # adf2md
 
+[![Tests](https://github.com/quiqueporta/adf2md/actions/workflows/tests.yml/badge.svg)](https://github.com/quiqueporta/adf2md/actions/workflows/tests.yml)
+![Lua](https://img.shields.io/badge/Lua-5.1%20|%205.2%20|%205.3%20|%205.4-blue.svg)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
+
 A Lua library to convert [Atlassian Document Format (ADF)](https://developer.atlassian.com/cloud/jira/platform/apis/document/structure/) to Markdown.
 
 ## Installation