CI: first draft GitHub Action

.github/workflows/main.yml

@@ -0,0 +1,19 @@
+---
+# configuration for GitHub Actions
+name: hardshare client
+on:
+    push:
+    pull_request:
+jobs:
+    build:
+        name: Build
+        runs-on: ubuntu-22.04
+        steps:
+            - uses: actions/checkout@v4
+            - name: Prepare to build
+              run: |
+                mkdir keys
+                touch keys/public.pem
+            - name: Run tests
+              run: |
+                cargo test