Explain why JDK is needed

Author: Happypig375

.github/workflows/Build all projects.yml

@@ -12,7 +12,7 @@ jobs:
       uses: actions/setup-dotnet@v1
       with:
         dotnet-version: '3.1.201'
-    - name: Setup JDK
+    - name: Setup JDK # Needed to run ANTLR for AngouriMath
       uses: actions/setup-java@v1
       with:
         java-version: '8'