replace travis CI with github actions (check syntax, check links)

- travis CI free plans were discontinued
- CI pipeline is similar to https://github.com/awesome-selfhosted/awesome-selfhosted-data and uses https://github.com/nodiscc/hecat
- the pipeline will not pass until https://github.com/awesome-foss/awesome-sysadmin/issues/416 has been fixed
- ref. https://github.com/awesome-foss/awesome-sysadmin/issues/405

Makefile

@@ -0,0 +1,29 @@
+SHELL := /bin/bash
+
+.PHONY: install # install build tools in a virtualenv
+install:
+	python3 -m venv .venv
+	source .venv/bin/activate && \
+	pip3 install wheel && \
+	pip3 install --force git+https://github.com/nodiscc/hecat.git@master
+
+.PHONY: import # import data from original list at https://github.com/awesome-foss/awesome-sysadmin
+import: install
+	rm -rf tags/ software/ platforms/
+	mkdir -p tags/ software/ platforms/
+	source .venv/bin/activate && \
+	hecat --config .hecat/import.yml
+
+.PHONY: awesome_lint # check data against awesome-sysadmin guidelines
+awesome_lint: install
+	source .venv/bin/activate && \
+	hecat --config .hecat/awesome-lint.yml
+
+.PHONY: url_check # check URLs for dead links or other connection problems
+url_check: install
+	source .venv/bin/activate && \
+	hecat --config .hecat/url-check.yml
+
+.PHONY: help # generate list of targets with descriptions
+help:
+	@grep '^.PHONY: .* #' Makefile | sed 's/\.PHONY: \(.*\) # \(.*\)/\1	\2/' | expand -t20