Implement a useful global help message

vultron/cmds/help.py

@@ -1,3 +1,4 @@
+import os
 import vultron.cmd
 import vultron.display
 
@@ -6,4 +7,25 @@ class Help(vultron.cmd.Command):
     self.needs_api_key = False
 
   def vultron_help(self):
-    print("stub help message here")
+    """This help message."""
+
+    prog = os.path.basename(self.prog)
+    cmds = vultron.cmd.Command.__subclasses__()
+
+    print(f"usage: {prog} [options] <cmd>")
+    print()
+    print("About:")
+    print("High-vultage API client for the vultrtual cloud.")
+    print()
+
+    # FIXME: print global options here
+
+    print("Commands:")
+
+    for cmd in cmds:
+      name = cmd.__name__.lower()
+
+      if cmd.__doc__ is None:
+        print(f"\t{name}")
+      else:
+        print(f"\t{name} - {cmd.__doc__}")