feat: Implement --help

lib/parsing/parser.dart

@@ -91,6 +91,44 @@ ParseResult extract(final List<String> args) {
   return result;
 }
 
+void _onHelpStage() {
+  final String help = '''
+usage: funkblubber [[-OPTIONS|URL]...]
+
+    A simple CLI for interaction with your Funkwhale account.
+
+    Options:
+      [-a|--album ID] Provide with album ID to download it. 
+
+      [-A|--artist ID] Provide with artist ID to download it and their albums.
+
+      [-p|--path PATH] Provide to explicitly define download directory.
+                       Assumed '.'.
+
+      [-d|--domain DOMAIN] Provide to explicitly define the host where your
+                           Funkwhale instance is. Required with -a, -A, and -u.
+                           Is not required if you download by a full URL.
+
+      Examples:
+        funkblubber https://my.funkwhale/library/tracks/10244/
+        Download album by URL to current folder.
+
+        funkblubber https://my.funkwhale/library/tracks/10244/ -p music
+        Download album by URL to local ./music folder.
+
+        funkblubber -A 152 -d my.funkwhale -p media/music/
+        Download everything by artist with ID 152 from a funkwhale instance
+        with my.funkwhale domain and save it to local ./media/music folder.
+
+        funkblubber --album 1423 -d my.funkwhale
+        Download album with ID 1423 from a funkwhale instance
+        with my.funkwhale domain and save it to current folder.
+
+  ''';
+
+  console.info(help);
+}
+
 StageResult _onEntityStage(
   final String arg,
   final ParseResult previousResult,
@@ -193,6 +231,11 @@ StageResult _onNothingStage(
     case '--domain':
       currentStage = ParsingStage.domain;
       break;
+    case '-h':
+    case '--help':
+      _onHelpStage();
+      currentStage = ParsingStage.nothing;
+      break;
     default:
       try {
         final Uri uri = Uri.parse(arg);