tools/doc: makefile: (auto-)document makefile targets with 'make help'

Makefile

@@ -1,6 +1,6 @@
 SHELL := /bin/bash
 
-.PHONY: install # install in a virtualenv
+.PHONY: install # install build tools in a virtualenv
 install:
 	python3 -m venv .venv
 	source .venv/bin/activate && \
@@ -27,3 +27,7 @@ build: install
 	source .venv/bin/activate && \
 	hecat build --source-directory ./ --output-directory awesome-selfhosted --output-file README.md
 	cd awesome-selfhosted && git diff --color=always
+
+.PHONY: help # generate list of targets with descriptions
+help:
+	@grep '^.PHONY: .* #' Makefile | sed 's/\.PHONY: \(.*\) # \(.*\)/\1	\2/' | expand -t20

README.md

@@ -63,13 +63,7 @@ If you are not comfortable sending a pull request, please copy/edit the template
 In [single page mode](https://github.com/awesome-selfhosted/awesome-selfhosted) the software will only appear under the first category in its `tags` list, so choose wisely.
 
 
-## Build the markdown list
-
-```bash
-make build
-```
-
-## Maintenance tasks
+## Maintenance
 
 **Rename a tag/category:** the tag must be renamed in the appropriate `tags/mytag.yml` file. All references to it must be updated in `tags/*.yml` and `software/*.yml`.
 
@@ -102,6 +96,16 @@ name: Java
 description: "[Java](https://en.wikipedia.org/wiki/Java_(programming_language)) is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible."
 ```
 
+**Automated tasks:**
+
+```bash
+$ make help
+install             install build tools in a virtualenv
+import              import data from original list at https://github.com/awesome-selfhosted/awesome-selfhosted
+process             apply automatic processing (gather github metadata)
+build               build markdown singlepage document from yaml data
+help                generate list of targets with descriptions
+```
 
 ## License