Add CI troubleshooting note for protobuf install failure

.github/workflows/backend.yml

@@ -46,7 +46,9 @@ jobs:
           java-version:  17
           distribution: 'temurin'
       - name: Install Protoc
-        run: sudo apt install -y protobuf-compiler
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y protobuf-compiler
       - name: Set up Python
         uses: actions/setup-python@v5
         with:

.github/workflows/codeql.yml

@@ -42,7 +42,9 @@ jobs:
           java-version: 17
           distribution: 'temurin'
       - name: Install Protoc
-        run: sudo apt install -y protobuf-compiler
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y protobuf-compiler
       - uses: actions/cache@v4
         with:
           path: ~/.m2/repository

README.md

@@ -278,3 +278,25 @@ limitations under the License.
 
 ## Acknowledgements
 The [Logo](https://wayang.apache.org/img/wayang.png) was donated by Brian Vera.
+
+## CI Troubleshooting
+
+If CI workflows fail during dependency installation with errors such as:
+
+```
+404 Not Found
+Failed to fetch protobuf packages
+```
+
+this may be caused by outdated package metadata on the CI runner.
+
+Ubuntu mirrors may remove older package versions, causing installations to fail.
+
+### Solution
+
+Refresh the package index before installation:
+```bash
+sudo apt-get update
+sudo apt-get install -y protobuf-compiler
+```
+This ensures the latest available package version is installed.