This simplifies integrating a remote bitcoind instance and
makes `bitcoin-cli` work with the remote node.
Add note regarding `whitelistedPort` to docs.
- Fix firewall.allowedTCPPorts settings
- Section `Allow bitcoind RPC connections`:
Set catch-all listen for `rpc.address` instead of `address`.
- rpc.allowip: Set subnet zero to fix allowing all addresses
- Move section `updating` from `usage.md` to `configuration.md` and
rename `usage.md` -> `services.md`.
`services.md` documents how enable and interact with node services.
- README: Move `docs` below `Get started`. The `docs` section is short and
should be easily accessible.
