I did this intentionally because from what I can tell for all other type the fields that you provide on creation are editable later on. This is not the case with repo comments (you can't change the position or file the comment belongs to). Because of this I felt it was confusing to have the struct as a parameter when only 1 of the user set fields can actually be edited. 

I do see your point about future additions to the repo comments (since we could then make these changes without breaking past behavior), so I'll go ahead and change it to take in a ```RepositoryComment``` and add a comment describing what fields a user can edit.