Documentation is missing global types

[filiptibell]

Some APIs such as process.spawn tell the user to look at docs for global types:

The third argument, `options`, can be passed as a dictionary of options to give to the child process.
Refer to the documentation for `ProcessSpawnOptions` for specific option keys and their values.

But global types are not currently included in the output for generated docs.

We should probably also show the luau type signature of functions and members somewhere.