lighthouse: add README and clean up plugin (#7316)

plugins/lighthouse/README.md

+# Lighthouse plugin
+
+This plugin adds commands to manage [Lighthouse](https://lighthouseapp.com/).
+
+To use it, add `lighthouse` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... lighthouse)
+```
+
+## Commands
+
+* `open_lighthouse_ticket <issue>` (alias: `lho`):
+
+  Opens the URL to the issue passed as an argument. To use it, add a `.lighthouse-url`
+  file in your directory with the URL to the individual project.
+
+  Example:
+  ```zsh
+  $ cat .lighthouse-url
+  https://rails.lighthouseapp.com/projects/8994
+
+  $ lho 23
+  Opening ticket #23
+  # The browser goes to https://rails.lighthouseapp.com/projects/8994/tickets/23
+  ```

plugins/lighthouse/lighthouse.plugin.zsh

-# To use: add a .lighthouse file into your directory with the URL to the
-# individual project. For example:
-# https://rails.lighthouseapp.com/projects/8994
-# Example usage: https://screencast.com/t/ZDgwNDUwNT
 open_lighthouse_ticket () {
   if [ ! -f .lighthouse-url ]; then
     echo "There is no .lighthouse-url file in the current directory..."
-    return 0;
-  else
-    lighthouse_url=$(cat .lighthouse-url);
-    echo "Opening ticket #$1";
-    open_command "$lighthouse_url/tickets/$1";
+    return 0
   fi
+
+  lighthouse_url=$(cat .lighthouse-url)
+  echo "Opening ticket #$1"
+  open_command "$lighthouse_url/tickets/$1"
 }
 
 alias lho='open_lighthouse_ticket'