Urllib3: Add time unit (seconds) to Timeout docs

[bgrant]

Neither the docs nor the docstrings say what unit timeouts should be provided in. Looking at the code, it appears to be "seconds", but it would be nice if the docs said this explicitly.

[sigmavirus24]

/joking

But how else will we convince people to read our beautiful beautiful source code?

[sethmlarson]

@bgrant Thanks for opening this issue! I agree that this would be a good addition. Do you think this is something you could accomplish?

[bgrant]

Sure- happy to.