update copyright, include description

LICENSE

@@ -1,5 +1,5 @@
 MIT License
-Copyright (c) <year> <copyright holders>
+Copyright (c) 2023 john melesky
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 

README.md

@@ -1,3 +1,30 @@
 # endless-sky-mode
 
-Emacs major mode for editing Endless Sky data files
+Emacs major mode for editing Endless Sky data files
+
+This mode does basically two things:
+
+  1. A bit of syntax highlighting. Not much, just keywords, strings,
+  and comments. The mode is not grammar-aware at all.
+  2. The tab key puts a tab character in. There's no smart
+  indentation, but tab characters are required for the data files, and
+  ~~most emacs users~~ I use spaces instead of tabs almost everywhere.
+
+Install and use as you usually do for things that aren't on any
+package archives. Because Endless Sky data files use the `.txt` file
+extension, I recommend invoking the mode manually when you start
+editing a file, rather than adding a hook and running the risk of
+getting the mode on random text files.
+
+
+# thanks
+
+Thanks to the varied authors of the EmacsWiki, particularly the
+[Derived Mode](https://www.emacswiki.org/emacs/DerivedMode) page.
+
+Thanks to /u/redblobgames for [help getting the tab key
+working](https://www.reddit.com/r/emacs/comments/10w9yii/how_do_you_create_a_derived_mode_with_tab/).
+
+Thanks to the [Endless Sky](https://endless-sky.github.io/) team, for
+a great game, and also great [documentation for
+creators](https://github.com/endless-sky/endless-sky/wiki).