[DOCS] Caveat for upgrading

[misilot]

• Which version of islandora are you using?
  2.0.1
• What user roles is this documentation intended for?

• Describe your documentation request.

A caveat exists in that, if islandora/islandora_defaults is required by any
other Composer package, then those packages may have to be updated first; for
example, it is known that there exist Drupal installation profiles that
specify a dependency on islandora/islandora_defaults (such as https://github.com/Islandora-Devops/islandora_install_profile_demo/blob/181a53bb230d7ced6e70e7746f0da567216ebbf7/composer.json#L157),
which would likely have to receive a treatment to strip out any references
from their configurations which explicitly bind to islandora_defaults
similar to our update hook, and to include updated requirements accordingly
in the root Composer project.

Are there directions what to do if this is the case?

• What implementations of islandora does this documentation request apply to?

• In what category in the existing documentation does this documentation belong?

Any related open or closed issues to this bug report?

Screenshots: