Mongodb hosting deployment

[cfnelson]

Added more details to the MongoDB hosting services to use with Galaxy section of the guide.

Changes made:

• Added recommendation for compose.io and MongoDB Atlas in addition to mLab
• Added more details on features to look out for when selecting a hosting service
• Added hyperlink to a step-by-step guide to setting up MongoDB Atlas for your Meteor app

I attempted to keep changes to a minimum, let me know if this is a significant change and I can update the CHANGELOG.md.

[apollo-cla]

@cfnelson: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[stubailo]

Yeah this should definitely be in the changelog. A big reason we have that is so that people who haven't looked in a while can catch up on what has been added. This is great new information, so it should get a spot there.

[cfnelson]

@stubailo Added a short description to the Changelog. Let me know what else I need to do to get this merged. 😄

[stubailo]

LGTM. I think it's good that the linked article makes a comparison for people.

[cfnelson]

@stubailo Thanks for merging! 😄 Let me know if you would like something like the comparison in the Meteor guides. Will be happy to make further contributions and/or create a MongoDB deployment section in the guide.

[stubailo]

Personally I'd rather not have that directly inside because it's very easy for it to get outdated. I think the list of things to look for is perfect.