cmd/go: add missing flag in UsageLine

Change-Id: I31689dc8de1f6b95bb35578b20533c63903f7258
GitHub-Last-Rev: 5bfee0535d
GitHub-Pull-Request: golang/go#47418
Reviewed-on: https://go-review.googlesource.com/c/go/+/337691
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Trust: Jay Conrod <jayconrod@google.com>
Trust: Russ Cox <rsc@golang.org>

src/cmd/go/alldocs.go

@@ -1078,7 +1078,7 @@
 //
 // Usage:
 //
-// 	go mod edit [editing flags] [go.mod]
+// 	go mod edit [editing flags] [-fmt|-print|-json] [go.mod]
 //
 // Edit provides a command-line interface for editing go.mod,
 // for use primarily by tools or scripts. It reads only go.mod;
@@ -1204,7 +1204,7 @@
 //
 // Usage:
 //
-// 	go mod init [module]
+// 	go mod init [module-path]
 //
 // Init initializes and writes a new go.mod file in the current directory, in
 // effect creating a new module rooted at the current directory. The go.mod file

src/cmd/go/internal/modcmd/edit.go

@@ -25,7 +25,7 @@ import (
 )
 
 var cmdEdit = &base.Command{
-	UsageLine: "go mod edit [editing flags] [go.mod]",
+	UsageLine: "go mod edit [editing flags] [-fmt|-print|-json] [go.mod]",
 	Short:     "edit go.mod from tools or scripts",
 	Long: `
 Edit provides a command-line interface for editing go.mod,

src/cmd/go/internal/modcmd/init.go

@@ -13,7 +13,7 @@ import (
 )
 
 var cmdInit = &base.Command{
-	UsageLine: "go mod init [module]",
+	UsageLine: "go mod init [module-path]",
 	Short:     "initialize new module in current directory",
 	Long: `
 Init initializes and writes a new go.mod file in the current directory, in