doc: document relay options

options.go

@@ -201,7 +201,12 @@ func AddrsFactory(factory config.AddrsFactory) Option {
 	}
 }
 
-// EnableRelay configures libp2p to enable the relay transport with configuration options.
+// EnableRelay configures libp2p to enable the relay transport with
+// configuration options. By default, this option only configures libp2p to
+// accept inbound connections from relays and make outbound connections
+// _through_ relays when requested by the remote peer. (default: enabled)
+//
+// To _act_ as a relay, pass the circuit.OptHop option.
 func EnableRelay(options ...circuit.RelayOpt) Option {
 	return func(cfg *Config) error {
 		cfg.RelayCustom = true
@@ -211,7 +216,7 @@ func EnableRelay(options ...circuit.RelayOpt) Option {
 	}
 }
 
-// DisableRelay configures libp2p to disable the relay transport
+// DisableRelay configures libp2p to disable the relay transport.
 func DisableRelay() Option {
 	return func(cfg *Config) error {
 		cfg.RelayCustom = true
@@ -220,8 +225,18 @@ func DisableRelay() Option {
 	}
 }
 
-// EnableAutoRelay configures libp2p to enable autorelay advertising; requires relay to
-// be enabled and the Routing option to provide an instance of ContentRouting.
+// EnableAutoRelay configures libp2p to enable the AutoRelay subsystem. It is an
+// error to enable AutoRelay without enabling relay (enabled by default) and
+// routing (not enabled by default).
+//
+// This subsystem performs two functions:
+//
+// 1. When this libp2p node is configured to act as a relay "hop"
+//    (circuit.OptHop is passed to EnableRelay), this node will advertise itself
+//    as a public relay using the provided routing system.
+// 2. When this libp2p node is _not_ configured as a relay "hop", it will
+//    automatically if it is unreachable (e.g., behind a NAT). If so, it will
+//    find, configure, and announce a set of public relays.
 func EnableAutoRelay() Option {
 	return func(cfg *Config) error {
 		cfg.EnableAutoRelay = true