gopls/internal/analysis/modernize/cmd/modernize: improve godoc

Change-Id: I34636fcac46744a80241e117cf02cf9192709f65
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674056
Auto-Submit: Alan Donovan <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: dolmen

gopls/internal/analysis/modernize/cmd/modernize/main.go

@@ -4,6 +4,8 @@
 
 // The modernize command suggests (or, with -fix, applies) fixes that
 // clarify Go code by using more modern features.
+//
+// See [golang.org/x/tools/gopls/internal/analysis/modernize] for details.
 package main
 
 import (