Suggest the user prepend to the file path

Suggest the user prepend the suggest new path to their existing file path to keep the terminal from finding outdated existing software first.

Author: mac10688

install.md

@@ -37,10 +37,10 @@ $ sudo apt-get update
 $ sudo apt-get install cabal-install-1.22 ghc-7.8.4 happy-1.19.5 alex-3.1.4
 ```
 
-Then add the following to your `$PATH` (bash\_profile, zshrc, bashrc, etc):
+Then prepend the following to your `$PATH` (bash\_profile, zshrc, bashrc, etc):
 
 ```
-~/.cabal/bin:/opt/cabal/1.22/bin:/opt/ghc/7.8.4/bin:/opt/happy/1.19.5/bin:/opt/alex/3.1.4/bin
+export PATH=~/.cabal/bin:/opt/cabal/1.22/bin:/opt/ghc/7.8.4/bin:/opt/happy/1.19.5/bin:/opt/alex/3.1.4/bin:$PATH
 ```
 
 *Optional:* You could also add `.cabal-sandbox/bin` to your path. Code that you