Add descriptions of new methods to the react-reconciler readme

[jackpope]

Add new reconciler methods since last breaking change to the README based on usage and comments.

[react-sizebot]

Comparing: fd0da3e...bdea3dc

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	168.88 kB	168.89 kB	=	52.68 kB	52.69 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	170.69 kB	170.69 kB	=	53.23 kB	53.24 kB
facebook-www/ReactDOM-prod.classic.js	=	591.32 kB	591.32 kB	=	103.85 kB	103.85 kB
facebook-www/ReactDOM-prod.modern.js	=	567.65 kB	567.65 kB	=	99.80 kB	99.80 kB
test_utils/ReactAllWarnings.js	Deleted	64.04 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	64.04 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Generated by 🚫 dangerJS against bdea3dc

[gnoff]

added some more details but looks good