Merge pull request #321 from babaorum/fix/documentation/oh-my-zsh-install

make Oh my zsh install works without ZSH_CUSTOM defined

README.md

@@ -35,7 +35,7 @@ Requirements: Zsh v4.3.11 or later
 1. Clone this repository into `$ZSH_CUSTOM/plugins` (by default `~/.oh-my-zsh/custom/plugins`)
 
     ```sh
-    git clone https://github.com/zsh-users/zsh-autosuggestions $ZSH_CUSTOM/plugins/zsh-autosuggestions
+    git clone https://github.com/zsh-users/zsh-autosuggestions ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-autosuggestions
     ```
 
 2. Add the plugin to the list of plugins for Oh My Zsh to load: