[Global/Eclipse] Make .project opt-in (#3305)

The project description file.

Global/Eclipse.gitignore

@@ -54,3 +54,7 @@ local.properties
 .cache-main
 .scala_dependencies
 .worksheet
+
+# Uncomment this line if you wish to ignore the project description file.
+# Typically, this file would be tracked if it contains build/dependency configurations:
+#.project