Ensure code blocks are formatted properly for GitHub (#1271)

README.md

@@ -13,23 +13,25 @@ version is 4.3.17.
 
   1. Launch Zsh:
 
-        zsh
+        `zsh`
 
   2. Clone the repository:
 
-        git clone --recursive https://github.com/sorin-ionescu/prezto.git "${ZDOTDIR:-$HOME}/.zprezto"
+        `git clone --recursive https://github.com/sorin-ionescu/prezto.git "${ZDOTDIR:-$HOME}/.zprezto"`
 
   3. Create a new Zsh configuration by copying the Zsh configuration files
      provided:
 
+        ```
         setopt EXTENDED_GLOB
         for rcfile in "${ZDOTDIR:-$HOME}"/.zprezto/runcoms/^README.md(.N); do
           ln -s "$rcfile" "${ZDOTDIR:-$HOME}/.${rcfile:t}"
         done
+        ```
 
   4. Set Zsh as your default shell:
 
-        chsh -s /bin/zsh
+        `chsh -s /bin/zsh`
 
   5. Open a new Zsh terminal window or tab.