f Clarify terms "known" and "supported"

Author: jkczyz

lightning/src/ln/features.rs

@@ -6,6 +6,11 @@
 //! defined internally by a trait specifying the corresponding flags (i.e., even and odd bits). A
 //! [`Context`] is used to parameterize [`Features`] and defines which features it can support.
 //!
+//! Whether a feature is considered "known" or "unknown" is relative to the implementation, whereas
+//! the term "supports" is used in reference to a particular set of [`Features`] from a peer. That
+//! is, a peer supports a feature if it advertises it (as either required or optional). And the
+//! implementation can interpet a feature if the feature is known to it.
+//!
 //! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
 //! [messages]: ../msgs/index.html
 //! [`Features`]: struct.Features.html