Provide instructions to create certificates using the openssl cli

[rido-min]

I need to create OPC certificates for testing and would prefer to do not have to install the Certificate Generator tool (that also requires to build per #18 ).

Will be great to have the openssl templates to produce the certificates with the OPC requirements.

BTW, browsing the docs [here]90https://opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User's%20Guide%20and%20Reference-QuickOPC/Providing%20Client%20Instance%20Certificate.html , it was not clear which are those requirements.

Is there a better doc describing the certificate requirements?