Provide SSL certificate entry doc section.

[phillxnet]

Thanks to Mark, via support email, for highlighting this issue. Under docs User Interface -> SSL Certificates we have a place-holder of "comming soon ...". It would be nice to have this contain at least a paragraph on the what & why along with pics of our existing interface to enter ones own SSL cert for the Web-UI.

https://rockstor.com/docs/interface/system/ssl_certificates.html

Visiting System -> SSL Certificate does provide a basic Web-UI to enter a user generated SSL certificate however:

upon clicking the "Update SSL Certificate" button we do have the following interface: