Add readme.md for each illuminate/projects

[lucasmichot]

Provides a readme.md for each Illuminate packages so that https://github.com/illuminate/auth/blob/master/readme.md will not be empty and will provide useful informations.
This readme file will also be accessible at https://github.com/laravel/framework/tree/master/src/Illuminate/Auth/readme.md

This PR comes with 2 files in /build:

• build/illuminate-readme.md is a template that be customized
• build/illuminate-readme.sh : generate all readme (except root readme.md file)

[franzliedke]

I think this is going in a good direction, however we need to take into account that some components already have their READMEs - at this point, only database and queue, as far as I know.

In fact, maybe we should start an initiative to create more detailed READMEs for some of the components where it makes sense to use them on their own. I'd be very open to help with that,

Still, 👍 for the idea!

[taylorotwell]

Would rather them just have useful information for each component where relevant. Some components I don't think make sense to really be documented outside of the main Laravel documentation.