emotty: add README (#8240)

plugins/emotty/README.md

+# emotty plugin
+
+This plugin returns an emoji for the current $TTY number so it can be used
+in a prompt.
+
+To use it, add emotty to the plugins array in your zshrc file:
+```
+plugins=(... emotty)
+```
+
+**NOTE:** it requires the [emoji plugin](https://github.com/robbyrussell/oh-my-zsh/tree/master/plugins/emoji).
+
+## Usage
+
+The function `emotty` displays an emoji from the current character set (default: `emoji`), based
+on the number associated to the `$TTY`.
+
+There are different sets of emoji characters available, to choose a different
+set, set `$emotty_set` to the name of the set you would like to use, e.g.:
+```
+emotty_set=nature
+```
+
+### Character Sets
+
+- emoji
+- loral
+- love
+- nature
+- stellar
+- zodiac
+
+Use the `display_emotty` function to list the emojis in the current character set, or
+the character set passed as the first argument. For example:
+
+```
+$ display_emotty zodiac
+<list of all the emojis in the zodiac character set>
+```