Recommendations for libraries using reqwest

[Sytten]

I think there should be some guidance for libraries using reqwest to make the life of end-users simpler.

I can think of:

• Disable default features, otherwise you force onto your user your choice of TLS library and roots
• Add indication in the readme that the user needs to add the reqwest dependency with TLS features they want to use
• ..... probably other things I am not thinking about

Otherwise right now it's a mess and each lib author decides which subset of feature they re-expose (rustls vs native for tls, webpki vs native for roots)