Add GitHub workflow to build and unit test

using a draft suggested by Copilot (but Copilot couldn't find the
correct libraries to install as dependencies, except for three of them).
And add its badge to README.

Author: sonertari

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: Build and Test
+
+on:
+  push:
+    branches: [ develop, master ]
+  pull_request:
+    branches: [ develop, master ]
+  workflow_dispatch:
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+
+    - name: Install dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y build-essential libevent-dev libssl-dev libnet1-dev libpcap-dev libsqlite3-dev check
+
+    - name: Build
+      run: make
+
+    - name: Run unit tests
+      run: make unittest

README.md

@@ -1,3 +1,5 @@
+[![Build and Test](https://github.com/sonertari/SSLproxy/actions/workflows/ci.yml/badge.svg)](https://github.com/sonertari/SSLproxy/actions/workflows/ci.yml)
+
 # SSLproxy - transparent SSL/TLS proxy for decrypting and diverting network traffic to other programs for deep SSL inspection
 
 Copyright (C) 2017-2025, [Soner Tari](mailto:sonertari@gmail.com).