Mention exporting repository providers in the Techniques/Database

[mayorandrew]

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] Other... Please describe:

Description

In @nestjs/core version before 6.3 you could inject typeorm repositories by importing a module which imports TypeOrmModule.forFeature, like so:

@Module({
  imports: [ TypeOrmModule.forFeature([ Photo ]) ]
})
export class PhotoModule {}

@Module({
  imports: [ PhotoModule ],
  providers: [ PhotoService ]
})
export class PhotoHttpModule {}

@Injectable()
export class PhotoService {
  constructor(@InjectRepository(Photo) private readonly photoRepo: Repository<Photo>) {}
  ...
}

Since version 6.3 you need to explicitly export typeorm repositories from PhotoModule. You can do that by exporting the whole TypeOrmModule module, like so:

@Module({
  imports: [ TypeOrmModule.forFeature([ Photo ]) ],
  exports: [ TypeOrmModule ]  // new
})
export class PhotoModule {}

Since this is not obvious I'd like this to be mentioned in the docs, so here is this PR which adds that information to the Techniques/Database page to the end of "Repository pattern" section.