Add MSDN link for certutil command

Signed-off-by: Hiroshi Hatake <hatake@clear-code.com>

plugins/output/forward.md

@@ -589,7 +589,7 @@ then add the following settings:
 Note that these configuration works for root certificate which is put in Windows Certstore.
 Currently, chained certificate is not supported.
 
-Certificate thumbprint is able to obtain with certutil command.
+Certificate thumbprint is able to obtain with [`certutil`](https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/certutil) command.
 Here is an example which uses a certificate that is generated by `fluent-ca-generate` command.
 
 ```