Add useful Makefile targets (install and serve)

Makefile

@@ -1,5 +1,9 @@
 .DEFAULT_GOAL := help
 
+.PHONY: install
+install: ## Install the dependencies to build the website
+	pip3 install --user -r requirements.txt
+
 .PHONY: build
 build: ## Build the website
 	python3 boop.py
@@ -8,6 +12,10 @@ build: ## Build the website
 clean: ## Clean output files
 	rm -rf ./output ./__pycache__
 
+.PHONY: serve
+serve: build ## Serve the website (development)
+	cd output && python3 -m http.server 8080
+
 .PHONY: help
 help:
 	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'