Updating the git page

This page might seem slightly big for a project called tl;dr, but git
has tons of commonly used options and I've kept all descriptions as
short but meaningful as possible (within 80 characters)
Removing unnecessary lines from the git page

Since the last change, I don't think we need to include git 'command' or
git version
Removing unnecessary git commands

Removing less frequently used git commands: reset and blame to make tldr pages serve their purpose of being short ;)
Merge pull request #142 from chirag64/master

Updating the git page by adding some git commands and removing previous unnecessary ones