Warn users about the need to import TLS certs into browser

As discussed with Dmytro Nochevnov, the KI in https://issues.redhat.com/browse/CRW-3030 needs to be documented in the docs.

When it's documented in the docs, the writer must close the KI issue https://issues.redhat.com/browse/CRW-3030.

Potentially applicable content for migrating into the new docs from the old docs:

https://www.eclipse.org/che/docs/che-7/end-user-guide/importing-certificates-to-browsers/

https://access.redhat.com/documentation/en-us/red_hat_codeready_workspaces/2.15/html-single/end-user_guide/index#importing-certificates-to-browsers_crw

//a general tip from Nick:

Import self-signed TLS certificates into your browser to avoid missing content in your workspace.