Extend some comments about bridge descriptors

crates/tor-guardmgr/src/bridge/descs.rs

@@ -18,6 +18,10 @@ use tor_netdoc::doc::routerdesc::RouterDesc;
 #[derive(Clone, Debug)]
 pub struct BridgeDesc {
     /// The inner descriptor.
+    ///
+    /// NOTE: This is wrapped in an `Arc<>` because we expect to pass BridgeDesc
+    /// around a bit and clone it frequently.  If that doesn't actually happen,
+    /// we can remove the Arc here.
     desc: Arc<RouterDesc>,
 }
 

crates/tor-guardmgr/src/bridge/relay.rs

@@ -6,7 +6,8 @@ use tor_linkspec::{ChanTarget, CircTarget, HasAddrs, HasRelayIds, RelayIdRef, Re
 
 use super::{Bridge, BridgeDesc};
 
-/// The information about a Bridge that is necessary to connect to it and relay traffic.
+/// The information about a Bridge that is necessary to connect to it and send
+/// it traffic.
 #[derive(Clone, Debug)]
 
 pub struct BridgeRelay {
@@ -23,7 +24,11 @@ pub struct BridgeRelay {
 }
 
 /// A BridgeRelay that is known to have its full information available, and
-/// which is therefore usable for circuits.
+/// which is therefore usable for multi-hop circuits.
+///
+/// (All bridges can be used for single-hop circuits, but we need to know the
+/// bridge's descriptor in order to construct proper multi-hop circuits
+/// with forward secrecy through it.)
 #[derive(Clone, Debug)]
 pub struct BridgeRelayWithDesc<'a>(
     /// This will _always_ be a bridge relay with a non-None desc.