Add subcommand pretty listing

bin/etherpump

@@ -1,9 +1,26 @@
 #!/usr/bin/env python3
 
+import os
 import sys
+from pathlib import Path
 
 from etherpump import __VERSION__
 
+
+def subcommands():
+    """List all sub-commands for the `--help` output."""
+    subcommands = []
+
+    all_files = os.listdir(Path().absolute() / 'etherpump' / 'commands')
+    modules = filter(lambda file: not file.startswith('__'), all_files)
+
+    for module in modules:
+        name = module.split('.py')[0]
+        subcommands.append(f'    {name}')
+
+    return '\n'.join(subcommands)
+
+
 usage = """
          _
         | |
@@ -18,23 +35,15 @@ Usage:
 
 where CMD could be:
 
-    pull
-    index
-    dumpcsv
-    gettext
-    gethtml
-    creatediffhtml
-    list
-    listauthors
-    revisionscount
-    showmeta
-    html5tidy
+{}
 
 For more information on each command try:
 
     etherpump CMD --help
 
-"""
+""".format(
+    subcommands()
+)
 
 try:
     cmd = sys.argv[1]