Update mongo.md

[Inaruslynx]

Added exports: [CatsService, MongooseModule], due to experiencing errors where AppModule would give error on CatModel. The above addition resolves issue.

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [x] Docs
• [ ] Other... Please describe:

What is the current behavior?

When code compiles an error is given Nest can't resolve dependencies of the CatService (?). Please make sure that the argument "CatModel" at index [0] is available in the AppModule context

Issue Number: N/A

What is the new behavior?

Code will compile.

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

[prateekkathal]

I don't think this is the intended solution the problem you are facing.

What do you exactly mean by:

due to experiencing errors where AppModule would give error on CatModel. The above addition resolves issue

Kindly provide some code to support your issue

[kamilmysliwiec]

CatsService should not be registered in AppModule