Provide easy way to use cli applications as clients

[elf-pavlik]

This steams out from: #139 (comment)

We should document how developers (unlikely regular users) can use command line tools and access data as clients.

During next AuthN meeting we may discuss client credentials flow. This might be enough to build a straight forward strategy to use CLI tools.

[elf-pavlik]

IMO this issue also depends on a resolution to solid/specification#504
Once resolved we need to describe publishing a WebID for the CLI client, which users should be able to do in their storage.
The user's Authorization Agent should be able to do it for them since they will still need to create an authorization for that CLI client. I'll draft the initial information sometime this month. This should not affect the spec; it can be explained in one of the primers. The flow I currently think of:

1. User generates a key pair for their CLI client
2. User authorizes their CLI client
   a) User provides a copy of the public key to their Authorization Agent
   b) Authorization Agent creates WebID document for that client, including its public key
   c) User gets WebID for their CLI client
3. User uses provided WebID and generated keypair with their CLI client (via config, shell variables, flags, etc.)

We should also pick up work on two issues below since someone using CLI might want to do some generic access and grant that CLI client escalated privileges.

• Finalize design for Trusted Consents and Trusted Grants #187
• Access needs for pod browser apps #237