add readme

README.md

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+# [fish-jabba][]
+
+[fish-jabba]:        https://github.com/2m/fish-jabba
+
+This is a [fish](https://fishshell.com) plugin for [jabba](https://github.com/shyiko/jabba). Together with packaging the [original shell integration code](https://github.com/shyiko/jabba/blob/1ca1e8a12f9e4c45530e2c652d79483678eef9c0/install.sh#L163-L172) required for jabba to work correctly, this plugin also includes autocompletion support for the following commands:
+
+* `use`
+* `install`
+* `uninstall`
+* `which`
+
+## Instalation
+
+If using [fundle](https://github.com/danhper/fundle) add the following to `~/.config/fish/config.fish`:
+
+```fish
+fundle plugin '2m/fish-jabba'
+```
+
+Reload fish shell and then run `fundle install`.