Determine and document minimum pip version for installation on Linux

[jonmmease]

Kaleido uses the manylinux2014 platform tag on Linux, and old versions of pip don't understand it. We should determine the minimum pip version needed, and document that in the README.

See #15

[WEGFan]

It should be pip >= 19.3 as documented here

[jonmmease]

Awesome, thanks!

[jonmmease]

Update: linux package now uses the manylinux1 platform tag.

[gvwilson]

Thanks for your interest in Kaleido. We are currently working on an overhaul that might address your issue - we hope to have news in a few weeks and will post an update then. Thanks - @gvwilson