Add description (and blog post) on Editor comments

[ronaldtse]

Editor comments (EDITOR: ...) differ from Internal comments (i.e. TODO:...).

Editor comments are used to indicate notes to the reader of a published document (e.g. a stage deliverable) that requires attention. These differ from internal comments such as "TODO" that are only meant for the author or the editing team.

From @rplews (can quote):

i would use them when i want a reader to see at ballot stage but i would have cleared all ms-word comments before the ballot... just leaving the zz help comment
like "backwards compatibility annex will be developed after comment resolutions are cleared" this way we dont get a bunch of comments saying "you forgot the backwards compat annex or add to the annex, etc..."

This is the documentation task for metanorma/metanorma-iso#682

[opoudjis]

Refer #602

[manuelfuenmayor]

@ronaldtse, as in #701, there is already a blog post and a section in the Author's Documentation about this subject:
Annotations now available in all Metanorma outputs
Annotations (editor notes, reviewer notes, to-dos)

Is it still necessary to create another blog post?