I am going to show you How to setup different How to create a document on Google Docs with option to Suggest an Edit
If you wish to allow other users to suggest edits but not to have the option to change file just press Share on the top.
Here select Anyone with the link can comment. Now users have the possibility to make comments and suggest edits.
Lets test this.
You see how i can edit the page and make suggestions. is quite easy and effective.