Add instructions to readme about how to install it

[andresmoschini]

(It comes from MakingSense/aspnet-home#6)

Maybe something like this but in the readme file.

Also, it could be useful to add a check-list in readme, for example:

Remember to do it after clone your seed:
[ ] - Rename namespaces.
[ ] - Remove unused middlewares and filters.
[ ] - Implement your own authentication handlrer.
[ ] - Replace or remove LICENSE file.
[ ] - Write your own README.md file and remove this one.