[compiler] Add readme for babel plugin

[poteto]

Stack from ghstack (oldest at bottom):

• -> [compiler] Add readme for babel plugin #29084

Adds a simple readme for the babel plugin with links to the docs.

[react-sizebot]

Comparing: a0eb265...094891a

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.js	=	6.66 kB	6.66 kB	+0.05%	1.82 kB	1.82 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	495.01 kB	495.01 kB	=	88.68 kB	88.68 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.67 kB	6.67 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	499.81 kB	499.81 kB	=	89.36 kB	89.36 kB
facebook-www/ReactDOM-prod.classic.js	=	592.16 kB	592.16 kB	=	104.15 kB	104.15 kB
facebook-www/ReactDOM-prod.modern.js	=	568.39 kB	568.39 kB	=	100.55 kB	100.55 kB
test_utils/ReactAllWarnings.js	Deleted	64.26 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	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Generated by 🚫 dangerJS against 094891a