installing dependent resources

[cmawhorter]

somewhat related to #72

service repos can be configured to ship a client that talks to the service view resource.json.client

need to think about how it's is going to work. yarn add some-service would install the client, but wouldn't update resource.json. adding some kind of install to bty would update resource and not package.

avoid:

• something like bty add some-service. no one wants to break their workflow
• the need to run bty refresh/sync to make sure package/resource match

if it's possible to have some kind of postinstall that invokes bty that'd be ideal. then when detecting a repo with a configured client, the workflow would be:

1. yarn add some-service
2. postinstall -> bty something
3. ::bty detects a valid resource.json::
4. betty detected some-service. would you like to add this as a resource in resource.json? y/N

If postinstall won't work (and it probably won't since npm deprecated it), another option would be to do it on bty update