Update specs/commandline/verify.md

Co-authored-by: Pritesh Bandi <priteshbandi@gmail.com>

specs/commandline/verify.md

@@ -40,7 +40,7 @@ Flags:
        --plain-http              registry access via plain HTTP
        --plugin-config strings   {key}={value} pairs that are passed as it is to a plugin, if the verification is associated with a verification plugin, refer plugin documentation to set appropriate values
   -u,  --username string         username for registry operations (default to $NOTATION_USERNAME if not specified)
-  -um, --user-metadata strings   {key}={value} pairs that must be present in the signature for successful verification if provided
+  -um, --user-metadata strings   user defined {key}={value} pairs that must be present in the signature for successful verification if provided
 ```
 
 ## Usage