Manual instructions on installation in-cluster devfile registry offline

[elsony]

/area documentation

Which area this documentation change is related to?
/area registry

Issue details

There is currently an item for implementing the ability to install a devfile registry offline (#329). Before that item is being implemented, we need to provide instructions for users to go through some manual steps to complete an offline registry installation.

The steps for doing an offline installation is described in #329 with the design doc https://docs.google.com/document/d/15PpUGiWOXjfQ5GtJFPHp0cG73jtpmw1H9AkCrnJVD2E/edit?usp=sharing

This document will basically mirror the steps described in the original design doc and make it available to our users.

This instruction should also be taken into account the work done on #499 so that after the user installed the registry, the tools should be able to get the list of devfile registries available on the cluster.

What mistake did you find / what is missing in the documentation?
See above.

Target Date: 06-30-2022

[michael-valdron]

This document will basically mirror the steps described in the original design doc and make it available to our users.

@elsony How did we want to present this document to our users?