Added tip for easier enabling of virtual environment to 'develop' makefile target.

(Redmine issue: #3387)

Makefile

@@ -195,7 +195,9 @@ develop: FORCE
 	@echo "\n$(CYAN)Your development environment is ready in `. $(VENV_PATH)/bin/activate && python -c 'import sys; print(sys.prefix)'`.$(NC)\n"
 	@echo "Please activate it manually with following command:\n"
 	@echo "\t$(ORANGE). $(VENV_PATH)/bin/activate$(NC)\n"
-	@echo "!!! Please keep in mind, that all makefile targets leave it up to you to activate the correct virtual environment !!!"
+	@echo "Consider adding following alias to your ~/.bashrc file for easier environment activation:\n"
+	@echo "\t$(ORANGE)alias entervenv='. venv/bin/activate'$(NC)\n"
+	@echo "$(BOLD)!!! Please keep in mind, that all makefile targets except this one ('develop') leave it up to you to activate the correct virtual environment !!!$(NC)"
 	@echo ""
 
 #
@@ -577,6 +579,7 @@ build-package-deb: FORCE
 	@grunt deb-build
 	@echo ""
 
+
 # Empty rule as dependency will force make to always perform target
 # Source: https://www.gnu.org/software/make/manual/html_node/Force-Targets.html
 FORCE: