cmd/go: fix 'go help go.mod' example

Dropped the example referred to in the text
when copying this text out of 'go help mod fix'.

Fixes #27083.

Change-Id: I63dfa3033fa2b2408019eef9d8b5a055aa803c57
Reviewed-on: https://go-review.googlesource.com/130140
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/alldocs.go

@@ -905,13 +905,15 @@
 // corresponding to this Go struct:
 //
 //     type Module struct {
-//         Path    string // module path
-//         Version string // module version
-//         Error   string // error loading module
-//         Info    string // absolute path to cached .info file
-//         GoMod   string // absolute path to cached .mod file
-//         Zip     string // absolute path to cached .zip file
-//         Dir     string // absolute path to cached source root directory
+//         Path     string // module path
+//         Version  string // module version
+//         Error    string // error loading module
+//         Info     string // absolute path to cached .info file
+//         GoMod    string // absolute path to cached .mod file
+//         Zip      string // absolute path to cached .zip file
+//         Dir      string // absolute path to cached source root directory
+//         Sum      string // checksum for path, version (as in go.sum)
+//         GoModSum string // checksum for go.mod (as in go.sum)
 //     }
 //
 // See 'go help modules' for more about module queries.
@@ -1617,7 +1619,19 @@
 //
 // The go command automatically updates go.mod each time it uses the
 // module graph, to make sure go.mod always accurately reflects reality
-// and is properly formatted.
+// and is properly formatted. For example, consider this go.mod file:
+//
+//         module M
+//
+//         require (
+//                 A v1
+//                 B v1.0.0
+//                 C v1.0.0
+//                 D v1.2.3
+//                 E dev
+//         )
+//
+//         exclude D v1.2.3
 //
 // The update rewrites non-canonical version identifiers to semver form,
 // so A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the

src/cmd/go/internal/modload/help.go

@@ -420,7 +420,19 @@ See 'go help mod edit'.
 
 The go command automatically updates go.mod each time it uses the
 module graph, to make sure go.mod always accurately reflects reality
-and is properly formatted.
+and is properly formatted. For example, consider this go.mod file:
+
+        module M
+
+        require (
+                A v1
+                B v1.0.0
+                C v1.0.0
+                D v1.2.3
+                E dev
+        )
+
+        exclude D v1.2.3
 
 The update rewrites non-canonical version identifiers to semver form,
 so A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the