Update e2e doc in `README.md` (#4503)
* Update e2e doc in `README.md`
* Update `ICreateClientOpts.cryptoStore` doc
* Apply first batch of suggestion
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
* Fix `cryptoStore` tsdoc in `client.ts`
* Changes in Initialization chapter.
* Add doc about deprecated methods in `MatrixClient`.
* Update SecretStorage doc
* Fis typos
* Improve e2e docs
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Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
