operators/join.rs: improve documentation for `join`
The copy/paste from join_map was a bit too eager, and while `join` is
nice for demos, `join_map` is usually what one wants in interesting
programs.
Tested by running `cargo doc --no-deps --open`.
@@ -28,7 +28,9 @@ use trace::TraceReader;
/// Join implementations for `(key,val)` data.
pub trait Join<G: Scope, K: Data, V: Data, R: Semigroup> {
- /// Matches pairs `(key,val1)` and `(key,val2)` based on `key` and then applies a function.
+ /// Matches pairs `(key,val1)` and `(key,val2)` based on `key` and yields pairs `(key, (val1, val2))`.
+ ///
+ /// The [`join_map`](Join::join_map) method may be more convenient for non-trivial processing pipelines.
///
/// # Examples
///
