Was hoping the read me contained on how to install this. First addon and I have no idea what I'm doing.

You need to download the latest version (for example from here), extract the archive, and place the MouselookHandler folder in the Interface\AddOns directory of your World of Warcraft installation. An "AddOns" button will appear on the character selection screen. You'll probably have to click it and then select the "Load out of date AddOns" checkbox (this is because I got tired of updating MouselookHandler's metadata every few months). This process is basically the same for all World of Warcraft interface addons.