medium_large not listed as a reserved image size in docs

[neychok]

I believe this ticket ​https://core.trac.wordpress.org/ticket/53538 should be here

Original description:
The medium_large image size was added in WordPress 4.4 as a new core image size:

​https://make.wordpress.org/core/2015/11/10/responsive-images-in-wordpress-4-4/

However, this is not listed as a reserved image size in the docs:

​https://developer.wordpress.org/reference/functions/add_image_size/#reserved-image-size-names

I think it should be added anywhere these reserved/core image sizes are mentioned.

[neychok]

I will start working on this.

[coffee2code]

Thanks for the report, @neychok!

The page has been updated.