Amended implementation-notes.md with link to Dan Abramov's post describing difference between React components, elements, and instances (#9388)
Amended implementation-notes.md with link to Dan Abramov's post describing difference between React components, elements, and instances (#9388)

* Amended implementation-notes.md to include a link to a blog post by Dan Abramov, explaining the difference between components, elements, and instances. An understanding of this distinction is crucial in tracing through Implementation pseudocode, and reading Dan's blog first may ease newcomers into understanding the implementation.

* adjusted wording to maintain stylistic consistency with rest of content, per @aweary's request

with-git/react,with-git/react,with-git/react,with-git/react,with-git/react,with-git/react,with-git/react