Refined the intro and installation sections.

Hello,

I saw the liquidprompt on Hackernew. 
I tried to give it a more catching intro to focus on 
why a new user should use it and how it helps them save time. 

I also tried to state the install section more clearly. 
This way users can testdrive it quicker. 

Congrats on the Hackernews list. 
I hope you accept these changes.