doc: document go tool pprof -http default change

For #74774.

Change-Id: I6a6a636c579fa95938021cc73d7d11a86f8a19a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/725540
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: prattmic

doc/next/3-tools.md

@@ -19,3 +19,8 @@ offer fixes to use newer features of the language and library.
 
 ### Cgo {#cgo}
 
+### Pprof {#pprof}
+
+<!-- go.dev/issue/74774 -->
+The `pprof` tool web UI, enabled with the `-http` flag, now defaults to the flame graph view.
+The previous graph view is available in the "View -> Graph" menu, or via `/ui/graph`.