Fixed git clone link in README.md

Made it so it clones using http
to avoid 
> git clone git@github.com:mcdevs/mark2.git
> Cloning into 'mark2'...
> The authenticity of host 'github.com (207.97.227.239)' can't be established.
> RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
> Are you sure you want to continue connecting (yes/no)? yes
> Warning: Permanently added 'github.com,207.97.227.239' (RSA) to the list of known hosts.
> Permission denied (publickey).
> fatal: The remote end hung up unexpectedly