API Documentation in README (#3904)

* Documentation

* immutable types / textEditor is a render function

* nit

* remove return types from titles

* fix incorrect generics

* nit

* tweaks

* tweak

* add missing imports

* tweak

* more tweaks

* tweaks

* tweaks

* add some performance notes

* remove ref line

* add links

* Update README.md

Co-authored-by: Aman Mahajan <[email protected]>

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Co-authored-by: Aman Mahajan <[email protected]>

Author: nstepien