Added linux CI build

.github/workflows/linux.yml

@@ -0,0 +1,22 @@
+name: Linux
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+    name: QtPBFImagePlugin
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install qtbase5-dev qtbase5-dev-tools qt5-qmake libprotobuf-dev protobuf-compiler zlib1g-dev
+      - name: Configure build
+        run: qmake gpxsee.pro
+      - name: Build project
+        run: make -j2