docs: improve doc for --no-upload option

This change adds documentation to the `no-upload` option
of the `cosign attest` command to clarify that when the option is
used, the produced attestation is written to STDOUT

Signed-off-by: Travis Truman <[email protected]>

Author: trumant

cmd/cosign/cli/attest.go

@@ -59,6 +59,9 @@ func Attest() *cobra.Command {
   # supply attestation via stdin
   echo <PAYLOAD> | cosign attest --predicate - <IMAGE>
 
+  # write attestation to stdout
+  cosign attest --predicate <FILE> --type <TYPE> --key cosign.key --no-upload true <IMAGE>
+
   # attach an attestation to a container image and honor the creation timestamp of the signature
   cosign attest --predicate <FILE> --type <TYPE> --key cosign.key --record-creation-timestamp <IMAGE>`,
 

cmd/cosign/cli/options/attest.go

@@ -74,8 +74,7 @@ func (o *AttestOptions) AddFlags(cmd *cobra.Command) {
 	_ = cmd.MarkFlagFilename("certificate-chain", certificateExts...)
 
 	cmd.Flags().BoolVar(&o.NoUpload, "no-upload", false,
-		"do not upload the generated attestation")
-
+		"do not upload the generated attestation, but send the attestation output to STDOUT")
 	cmd.Flags().BoolVarP(&o.Replace, "replace", "", false,
 		"")