Add install instructions.

README.adoc

@@ -1,8 +1,20 @@
 = download-yt-feeds
-:url-ytdl-format: https://github.com/ytdl-org/youtube-dl/#format-selection
+:url-zsh: https://www.zsh.org/
+:url-ytdl: https://github.com/ytdl-org/youtube-dl
+:url-ytdl-format: {url-ytdl}/#format-selection
 
 Download YouTube-feeds like they are podcasts. Files will be put in `<download_dir>/channel/title.extension`.
 
+== Install
+
+Put `download-yt-feeds` somewhere in your `${PATH}` and make it executable.
+
+=== Dependencies
+
+* Linux (\*BSD and other UNIXes should work, but I haven't tested)
+* link:{url-zsh}[Zsh]
+* link:{url-ytdl}[youtube-dl]
+
 == Configuration
 
 The configuration directory is `${XDG_CONFIG_HOME}/download-yt-feeds` or, if