Update INSTALL.md

I lost myself in the internet abyss because of this imprecision. It might be helpful for the new noob trying to install that great tweak. :)

INSTALL.md

@@ -24,7 +24,7 @@
     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:
+2. Add the plugin to the list of plugins for Oh My Zsh to load (inside `~/.zshrc`):
 
     ```sh
     plugins=(zsh-autosuggestions)