x/exp/cmd/gorelease: add usage

This makes it a bit easier to figure out how to use, rather than inferring from
fairly long main text. :)

Change-Id: Ie7a0c1cf3b77db2537964a77077b7f4ca80c4a49
Reviewed-on: https://go-review.googlesource.com/c/exp/+/251458
Run-TryBot: Jean de Klerk <deklerk@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

cmd/gorelease/gorelease.go

diff --git a/cmd/gorelease/gorelease.go b/cmd/gorelease/gorelease.go
index c525155..8533d76 100644
--- a/cmd/gorelease/gorelease.go
+++ b/cmd/gorelease/gorelease.go
@@ -5,6 +5,24 @@
 // gorelease is an experimental tool that helps module authors avoid common
 // problems before releasing a new version of a module.
 //
+// Usage:
+//
+//    gorelease [-base={version|none}] [-version=version]
+//
+// Examples:
+//
+//    # Compare with the latest version and suggest a new version.
+//    gorelease
+//
+//    # Compare with a specific version and suggest a new version.
+//    gorelease -base=v1.2.3
+//
+//    # Compare with the latest version and check a specific new version for compatibility.
+//    gorelease -version=v1.3.0
+//
+//    # Compare with a specific version and check a specific new version for compatibility.
+//    gorelease -base=v1.2.3 -version=v1.3.0
+//
 // gorelease analyzes changes in the public API and dependencies of the main
 // module. It compares a base version (set with -base) with the currently
 // checked out revision. Given a proposed version to release (set with