Editor docs edit link points to raw github URLs

[milana_cap]

Github edit link for block editor dev docs is pointing to wrong URL.

For examlpe, in old handbook:
​https://wordpress.org/gutenberg/handbook/

it's going to:
​https://github.com/WordPress/gutenberg/edit/master/docs/readme.md

While in new one:
​https://developer.wordpress.org/block-editor/handbook/

it goes to:
​https://raw.githubusercontent.com/WordPress/gutenberg/master/docs/readme.md

[coffee2code]

In 8701:

Developer: Fix Block Editor handbook edit links.

Temporary fix while the manifest specifies a link to the raw file instead of the expected non-raw link.

Fixes #4419.