add CI workflow and initial main.c file with a simple main function

.gitea/workflows/ci.yml

@@ -1,8 +1,10 @@
 name: First CI
 on: [push]
+
 jobs:
   build:
       runs-on: ubuntu-latest
       steps:
-        - name: Printing hello
-          run: echo "Hello, 🌍"
+        - uses: actions/checkout@v4
+        - name: build using gcc
+          run: gcc -wall -werror main.c

main.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main()
+{
+    pritnf("Halo, welt!");
+    return 0;
+}