Clarify a bit web integration document (#122)

* Clarify a bit web integration document

* Rewrite sentence that makes it looks like this is not useful for the general web developer

* Nuke most of the registration context mentions

* Remove streams comment

* Remove remaining registration context reference

* Remove comment

* Update observers to match current thinking

* Update WEB-INTEGRATION.md

Co-authored-by: Andreu Botella <andreu@andreubotella.com>

* Updates

* Fix headings

* Update WEB-INTEGRATION.md

Co-authored-by: Andreu Botella <andreu@andreubotella.com>

* Update WEB-INTEGRATION.md

Co-authored-by: Andreu Botella <andreu@andreubotella.com>

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Co-authored-by: Andreu Botella <andreu@andreubotella.com>

Author: nicolo-ribaudo