Writing doc about I/O SQL features. See #2541

[garaud]

Hi there,

I wrote some contents about I/O SQL pandas features:

• some examples about the read_frame function with SQLite ;
• list other functions such as tquery (without example) ;
• write a tiny note about write_frame function.

I'm not sure about the title of this section. Any proposal is welcome ! Don't hesitate to comment the content (typo, misunderstanding, ...)

Cheers

Damien G.

[garaud]

closes #2541

[wesm]

thanks!