rcmgr: miscellaneous feedback on the design/interface

Nobody has claimed this yet.

Below are things that stood out when reading the README with fresh eyes.

Feedback on https://github.com/libp2p/go-libp2p-resource-manager/blob/master/README.md
1. (minor) The DAG diagram is hard for me to parse. I think it we want to show a DAG, it's better to use something like graphviz. It looks like that can be done cleanly with Github following something like https://github.com/TLmaK0/gravizo
2. We are inlining default limits. I think we should remove them and point to https://github.com/libp2p/go-libp2p-resource-manager/blob/master/limit_defaults.go because that is that is the source of truth and is complete. For example, the inlined limits are missing "DefaultPeerBaseLimit"

Feedback on https://github.com/libp2p/go-libp2p-resource-manager/blob/master/limit_defaults.go
1. I was surprised to see ServicePeer* and ProtocolPeer* limits since I don't think I saw them in the readme.
2. Why do we need to define a "BaseLimit" and "Memory" separately. Maybe this design choice should be discussed in the readme?

Start with README.md and limit_defaults.go, comparing the documented limits and the source-of-truth defaults. Review the DAG diagram and the explanations of ServicePeer*, ProtocolPeer*, BaseLimit, and Memory. Confirm the intended documentation scope with maintainers; done means the README accurately reflects the defaults and explains the relevant design choices.

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