[Makefile] add help and more idiomatic makefile

- Add `help` directive
- Add `clean` and `all` directives
- Rename `tests` to `test`

Makefile

@@ -1,17 +1,22 @@
-.PHONY: format lint tests tests_watch integration_tests
+.PHONY: all clean format lint test test_watch integration_tests help
 
+all: help
+	
 coverage:
 	poetry run pytest --cov \
 		--cov-config=.coveragerc \
 		--cov-report xml \
 		--cov-report term-missing:skip-covered
 
+clean: docs_clean
+
 docs_build:
 	cd docs && poetry run make html
 
 docs_clean:
 	cd docs && poetry run make clean
 
+
 docs_linkcheck:
 	poetry run linkchecker docs/_build/html/index.html
 
@@ -25,11 +30,24 @@ lint:
 	poetry run isort . --check
 	poetry run flake8 .
 
-tests:
+
+test:
 	poetry run pytest tests/unit_tests
 
-tests_watch:
+test_watch:
 	poetry run ptw --now . -- tests/unit_tests
 
 integration_tests:
 	poetry run pytest tests/integration_tests
+
+help:
+	@echo '----'
+	@echo 'coverage       		- run unit tests and generate coverage report'
+	@echo 'docs_build     		- build the documentation'
+	@echo 'docs_clean     		- clean the documentation build artifacts'
+	@echo 'docs_linkcheck 		- run linkchecker on the documentation'
+	@echo 'format 		  		- run code formatters'
+	@echo 'lint           		- run linters'
+	@echo 'tests 		  		- run unit tests'
+	@echo 'tests_watch    		- run unit tests in watch mode'
+	@echo 'integration_tests 	- run integration tests'