Update README.md

[ERbittuu]

Import MaterialProgressBar instead of LinearProgressBar

[Recouse]

Hello,
Thank you for the contribution.
I think it will be better, if you mention that the name of the framework depends on a dependency manager. MaterialProgressBar only for CocoaPods.

[ERbittuu]

It is just typing mistake on example code from README.md

[Recouse]

I mean if you use it with Carthage or SPM, the name of the framework will be LinearProgressBar.
I couldn't use that name for CocoaPods because it was already taken.