Update Ambient Module section in modules.md

[unional]

This section under Ambient Module should be removed:

... We could define each module in its own .d.ts file with top-level export declarations, but it’s more convenient to write them as one larger .d.ts file. To do so, we use a construct similar to ambient namespaces, but we use the module keyword and the quoted name of the module which will be available to a later import

This will prohibit renaming at consumption and create conflict when there are two versions of the package is in used.

Related to:
microsoft/TypeScript#7398

See example on how it will fail:
https://github.com/typings/typings/blob/master/docs/external-modules.md

[DanielRosenwasser]

The entire section sort of needs a rewrite. I'll admit that I unfortunately haven't gotten the chance to really take a look at #185, but the work should be done there.

[unional]

That's a big rewrite. 😄

[unional]

Collaborative editing markdown is much easier on hackpad then through PR. 😛