chore: Set help target as default goal

Add explicit comments explaining the purpose of the `help` target and `.DEFAULT_GOAL`.
This improves readability and makes the Makefile's behavior more transparent.

PR-393#393

Author: echoix

Makefile

@@ -2,6 +2,13 @@
 # the `make` command will point at the `scripts/make` shell script.
 # This Makefile is just here to allow auto-completion in the terminal.
 
+# The first target in the makefile is the default goal when no targets are specified.
+# Having "help:" here above without any rule (nothing to do specified with a tab)
+# only adds dependencies to that target, that is defined through "$(actions):".
+# .DEFAULT_GOAL is not necessary here, but is really explicit about what is going on.
+help:
+.DEFAULT_GOAL: help
+
 actions = \
 	allrun \
 	changelog \