Share Lighthouse results in README

[addyosmani]

URL: https://react-shrine.firebaseapp.com/

WPT:
Regular 3G: https://www.webpagetest.org/result/180207_G7_4bb4eb32230a2ebf8252b1f8b4600895/
Slow 3G: https://www.webpagetest.org/result/180207_CS_1d42be94592318dfd875e86e35fff314/
4G: https://www.webpagetest.org/result/180207_6T_fd99598f3d43997715639d4a0d51ec76/

[divyanshu-rawat]

@addyosmani is this issue open to work on?