Licence in help

Program.cs

@@ -413,7 +413,23 @@ class Program
 		var configOption = new Option<FileInfo>
 			("--config", "Path to configuration file.");
 		configOption.AddAlias("-c");
-		var rootCommand = new RootCommand("An alternative implementation for i3 status bar generating.");
+		var rootCommand = new RootCommand(
+@"i3csstatus - Alternative generator of i3 status bar written in c#
+
+(c)   2022 Jiri Kalvoda <jirikalvoda@kam.mff.cuni.cz>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.");
 		rootCommand.AddGlobalOption(configOption);
 
 		var c_plainText = new Command("plain-text", "Print status bar as plain text.");