Update IGListDiffable and Equality.md
Update IGListDiffable and Equality.md

Summary:
Some minor tweaks and improvements to this guide. 😄
Closes https://github.com/Instagram/IGListKit/pull/265

Differential Revision: D4235752

Pulled By: jessesquires

fbshipit-source-id: 03adec7750ac8ded23542db97b9506ff7dc00adf

Instagram/IGListKit,charles0126dev/IGListKit,Instagram/IGListKit,Sherlouk/IGListKit,Sherlouk/IGListKit,charles0126dev/IGListKit,Instagram/IGListKit,Sherlouk/IGListKit,zhubofei/IGListKit,dshahidehpour/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,dshahidehpour/IGListKit,zhubofei/IGListKit,charles0126dev/IGListKit,zhubofei/IGListKit,dshahidehpour/IGListKit