build: keep geth-sources.jar build result for JavaDoc (#21596)

* ci: tooltips for javadoc for mobile app

* f space

Makefile

@@ -24,7 +24,9 @@ android:
 	$(GORUN) build/ci.go aar --local
 	@echo "Done building."
 	@echo "Import \"$(GOBIN)/geth.aar\" to use the library."
-
+	@echo "Import \"$(GOBIN)/geth-sources.jar\" to add javadocs"
+	@echo "For more info see https://stackoverflow.com/questions/20994336/android-studio-how-to-attach-javadoc"
+	
 ios:
 	$(GORUN) build/ci.go xcode --local
 	@echo "Done building."