document generics in readme (#12)

README.md

@@ -3,11 +3,12 @@
 [![GoDoc](https://godoc.org/resenje.org/singleflight?status.svg)](https://godoc.org/resenje.org/singleflight)
 [![Go](https://github.com/janos/singleflight/workflows/Go/badge.svg)](https://github.com/janos/singleflight/actions?query=workflow%3AGo)
 
-Package singleflight provides a duplicate function call suppression
-mechanism similar to [golang.org/x/sync/singleflight](https://pkg.go.dev/golang.org/x/sync/singleflight) but with support
-for context cancelation. The context passed to the callback function is a context that preserves all values
-from the passed context but is cancelled by the singleflight only when all
-awaiting caller's contexts are cancelled.
+Package singleflight provides a duplicate function call suppression 
+mechanism similar to [golang.org/x/sync/singleflight](https://pkg.go.dev/golang.org/x/sync/singleflight) but with:
+
+- support for context cancelation. The context passed to the callback function is a context that preserves all values
+from the passed context but is cancelled by the singleflight only when all awaiting caller's contexts are cancelled.
+- support for generics.
 
 ## Installation
 

singleflight.go

@@ -15,6 +15,8 @@ import (
 
 // Group represents a class of work and forms a namespace in
 // which units of work can be executed with duplicate suppression.
+// K is the type of the key used for deduplication, and V is
+// the return value of the work function.
 type Group[K comparable, V any] struct {
 	calls map[K]*call[V] // lazily initialized
 	mu    sync.Mutex     // protects calls