This should give support for a flag such as -o which allows the user to add a custom output file name.

Currently the -p flag will only work with relative paths. This is a node-js constraint. We should support some way of making it recognizable.

rel: nodejs/node#684

There are a couple of quick usage examples already. I think it'd be good to have an example for each of the common use cases; nothing fancy, just something like (changing out naff bits):

Example CLI Usage

List available chains

generate-type-bundle -a

Generate types bundle for a specific chain

Pass -s or --specName multiple times to output types for multiple chains into the same file.

generate-type-bundle -p ~/Desktop/example/types -s moonbeam

Generate and use types bundle in Sidecar

...

This should accept multiple chains, not exactly sure if yargs can parse it or can accept an array of values, but i think regardless we should probably do some custom parsing.

The format would be like -s moonbeam for a single chain, or -s moonbeam,karura,acala for multiple chains.