Document Reporters can create merge requests

Reported as a security issue originally, but recuded to a docs fix, it
is possible for Reporters to create a merge request by first forking
the project and then opening a merge request. This is consistent with
the fact that Reporters have permission to view and pull the repository
and that the point of the forking workflow is to allow anyone to
contribute while only requiring read permissions.

Additionally, it is possible for Guests to contribute to public
projects in the same way.

doc/user/permissions.md

@@ -73,7 +73,7 @@ The following table depicts the various user permission levels in a project.
 | See a commit status                               |         | ✓          | ✓           | ✓        | ✓      |
 | See a container registry                          |         | ✓          | ✓           | ✓        | ✓      |
 | See environments                                  |         | ✓          | ✓           | ✓        | ✓      |
-| See a list of merge requests                      |         | ✓          | ✓           | ✓        | ✓      |
+| See a list of merge requests                      | ✓ (*1*) | ✓          | ✓           | ✓        | ✓      |
 | View project statistics                           |         | ✓          | ✓           | ✓        | ✓      |
 | View Error Tracking list                          |         | ✓          | ✓           | ✓        | ✓      |
 | Pull from [Conan repository](packages/conan_repository/index.md), [Maven repository](packages/maven_repository/index.md), or [NPM registry](packages/npm_registry/index.md) **(PREMIUM)** |         | ✓          | ✓           | ✓        | ✓      |
@@ -83,7 +83,7 @@ The following table depicts the various user permission levels in a project.
 | Push to non-protected branches                    |         |            | ✓           | ✓        | ✓      |
 | Force push to non-protected branches              |         |            | ✓           | ✓        | ✓      |
 | Remove non-protected branches                     |         |            | ✓           | ✓        | ✓      |
-| Create new merge request                          |         |            | ✓           | ✓        | ✓      |
+| Create new merge request                          | ✓ (*1*) | ✓          | ✓           | ✓        | ✓      |
 | Assign merge requests                             |         |            | ✓           | ✓        | ✓      |
 | Label merge requests                              |         |            | ✓           | ✓        | ✓      |
 | Lock merge request threads                        |         |            | ✓           | ✓        | ✓      |