updated per code review

Signed-off-by: Patrick Zheng <patrickzheng@microsoft.com>

specs/commandline/sign.md

@@ -26,7 +26,7 @@ The file content, i.e. the file blob, is signed.
 Upon successful signing, the generated signature is stored to user specified signature path in file system. The output message is printed out as following:
 
 ```text
-Successfully signed <target_file>, stored signature at <signature_file>
+Successfully signed <target_file> and created signature at <signature_file>
 ```
 
 ## Outline
@@ -183,10 +183,10 @@ notation sign --file --signature <signature_path> <target_file_path>
 Examples of successful signing:
 ```console
 $ notation sign --file ./myFile.txt 
-Successfully signed ./myFile.txt, stored signature at ./myFile.sig
+Successfully signed ./myFile.txt and created signature at ./myFile.sig
 
 $ notation sign --file --signature ./mySignature.sig ./myFile.txt 
-Successfully signed ./myFile.txt, stored signature at ./mySignature.sig
+Successfully signed ./myFile.txt and created signature at ./mySignature.sig
 ```
 
 ### [Experimental] Sign container images stored in OCI layout directory