Add clarity to WPMS documentation about requesting multisites (#9332)

* add explanation about why WP sites can't just magically become multisites

* update the custom upstream intro to add glossary terms
I am hypothesizing that glossary terms are added based on the <dfn> tag. I am further hypothesizing that if we leave the markdown syntax on this page intact, the new glossary terms would not be added correctly, therefore I have converted all the markdown bullets to html list items.

I have added "framework" on this page because it makes the most sense to be included on a page about upstreams.

* a little more clarity about what settings

* remove the note, rephrase

* remove html formatting
didn't work for the glossary

* use headings and p tags

* use upstream framework as the term instead

* rename upstream framework to site framework
more in line with what exists in the dashboard

* site framework doesn't create the glossary page
go back to upstream framework but describe as "site framework" in parenthetical

* use em tags for emphasis

* link to framework in the glossary

* add space

Co-authored-by: Phil Tyler <[email protected]>

* fix the link

* clarify wpms upstream creation

Co-authored-by: Rachel <[email protected]>

* simplify existing wpms conversion description

Co-authored-by: Rachel <[email protected]>

* support creates the upstream, not the multisite itself

* Minor phrasing change to WPMS upstream access

* don't say "wordpress network"

* Update source/content/guides/multisite/01-introduction.md

Co-authored-by: Rachel <[email protected]>

* Apply suggestions from code review

Co-authored-by: Rachel <[email protected]>

---------

Co-authored-by: Phil Tyler <[email protected]>
Co-authored-by: Rachel <[email protected]>
Co-authored-by: Chris Charlton <[email protected]>

source/content/guides/multisite/01-introduction.md

@@ -41,17 +41,17 @@ We do not support uses of WordPress Multisite that run functionally-different or
 ## Request a WordPress Multisite
 WordPress Multisite requires a special configuration that is only available to select customers. Access to WordPress Multisite requires a Gold, Platinum, or Diamond level [Workspace plan](https://pantheon.io/plans/pricing).
 
-By default, Pantheon employees must create new Multisites on your behalf. Reach out to your account manager to request site creation for a new WordPress Multisite.
+Pantheon employees must enable a WordPress Multisite custom upstream on your behalf so your team can create new Multisites self-serve in your professional workspace. This is because WordPress Multisites use the `wordpress_network` [framework](/glossary/#framework), which includes Multisite specific Nginx configurations and differs from the default `wordpress` framework. Reach out to your account manager to get started, or if you don't have an account manager, you can [contact sales](https://pantheon.io/contact-us).
 
-If you want to create new WordPress Multisites self-serve and on-demand in the Pantheon Dashboard, reach out to your account manager and request a [Custom Upstream](/guides/custom-upstream) for your workspace based on Pantheon's WordPress Multisite framework.
 
-Existing WordPress sites cannot be converted to a multisite, however they can be [migrated](/migrate-wordpress-multisite).
+Existing WordPress sites cannot be converted to WordPress Multisites (since they are different frameworks), however you can spin up a new WordPress Multisite and then [manually migrate](/migrate-manual) the code, database and files from your existing site. 
 
-If you don't have an account manager, you can [contact sales](https://pantheon.io/contact-us).
 
 
  ## More Resources
 
+- [Migrate a WordPress Multisite onto Pantheon](/migrate-wordpress-multisite)
+
 - [WordPress on Pantheon Quick Start Guide](/guides/wordpress-pantheon/)
 
 - [Supported WordPress Versions](/supported-wp)