Add bespoke help descriptions

Makefile

@@ -1,36 +1,42 @@
 .PHONY: build events dev stop help prep lint format
 
-help:
-	@echo "Available commands:"
-	@echo "  make prep    - Create venv and install requirements"
-	@echo "  make events  - Update site from CSV (build pages + images)"
-	@echo "  make dev     - Start development server"
-	@echo "  make stop    - Stop development server"
-	@echo "  make build   - Full website build sequence"
-	@echo "  make help    - Show this help message"
+requirements += python3
+requirements += nginx
 
-prep:
+help:
+	@awk 'BEGIN {FS = ":.*?## "} /^[0-9a-zA-Z._-]+:.*?## / {printf "\033[36m%s\033[0m : %s\n", $$1, $$2}' $(MAKEFILE_LIST) | sort | column -s ':' -t
+
+.PHONY: check
+check: ## Check you have the required dependencies
+	@$(foreach dep, $(requirements), type $(dep) >/dev/null || echo "Install $(dep)." ; )
+
+prep: ## Create venv and install requirements
 	python3 -m venv .venv
 	./.venv/bin/pip install --upgrade pip
 	./.venv/bin/pip install -r requirements.txt
 
-build:
+build: ## Full website build sequence
 	./.venv/bin/python atom_gen.py
 	./.venv/bin/python prep.py
 	./.venv/bin/python build_pages.py
 
-events:
+events: ## Update site from CSV (build pages + images)
 	./.venv/bin/python build_pages.py
 	./.venv/bin/python image_poster.py
 
-dev:
+dev: ## Start development server
 	nginx -p . -c nginx.dev.conf
 
 stop:
 	nginx -p . -c nginx.dev.conf -s stop
 
-lint:
+lint: ## Check syntax
 	./.venv/bin/flake8 . --config .flake8 --exclude .venv
 
 format:
 	./.venv/bin/black .
+
+.PHONY: clean
+clean: ## Remove generated files.
+	$(RM) $(defaults)
+