(DOCSP-45121) Adds reason for upgrading to min supported version. (#518)

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- [DOCSP-45121](https://jira.mongodb.org/browse/DOCSP-45121)
-
[STAGING](https://deploy-preview-518--10gen-docs-ops-manager.netlify.app/tutorial/upgrade-ops-manager/)

### Self-Review Checklist

- [ ]
[Define](https://wiki.corp.mongodb.com/display/DE/Taxonomy+tagging+instructions)
taxonomy
[values](https://wiki.corp.mongodb.com/display/DE/Docs+Taxonomy) at top
of page.
- [ ] Add genre facets (tutorial or reference), as in this [example
PR](10gen/cloud-docs#5042).
- [ ] Add programmingLanguage (if necessary).
- [ ] Add meta keywords (if necessary).
- [ ] Resolve any new warnings or errors in the build.
- [ ] Proofread for spelling and grammatical errors.
- [ ] Check staging for rendering issues.
- [ ] Confirm links are working.

Author: erabil-mdb

source/includes/admonitions/warning/om8-manages-mdb-6-or-later.rst

@@ -2,6 +2,8 @@
 
    |onprem| 8.0 doesn't support MongoDB 4.2 and earlier. If you're using
    MongoDB 4.2 or earlier and want to upgrade to |onprem| 8.0, you must
-   upgrade to at least MongoDB 4.4. However, we recommend that you upgrade
+   upgrade to at least MongoDB 4.4. If you don't upgrade to at least MongoDB 4.4, 
+   |onprem| fails :ref:`pre-flight checks <fix-local-mode-start-failure>` and won't start. 
+   After upgrading to at least MongoDB 4.4, we still recommend that you upgrade
    to at least MongoDB 6.0 before upgrading to |onprem| 8.0.