update the custom upstream intro to add glossary terms

source/content/guides/custom-upstream/01-custom-upstream.md

@@ -126,20 +126,38 @@ Support for Custom Upstreams requires that the externally hosted upstream reposi
 
 Here are definitions for commonly used terms:
 
-- **Upstream**: A repository that acts as a parent for another repository, like [Pantheon's WordPress Upstream](https://github.com/pantheon-systems/wordpress). The next two definitions are specific types of Upstreams.
+### Upstream
 
-- **Custom Upstream**: A repository restricted to members of an organization, containing a common codebase for new sites. This type of repository is a child repository to Pantheon's core upstreams ([WordPress](https://github.com/pantheon-systems/wordpress),[Drupal (Latest Version)](https://github.com/pantheon-upstreams/drupal-composer-managed), [Drupal 7](https://github.com/pantheon-systems/drops-7)) and acts as a parent for site level repositories.
+<p>An <dfn id="upstream">upstream</dfn> is a repository that acts as a parent for another repository, like <a href="https://github.com/pantheon-systems/wordpress">Pantheon's WordPress Upstream</a>.</p>
 
-- **Public Upstream**: A repository that is open to all Pantheon users which contains a common codebase for new sites, like [Panopoly](https://github.com/populist/panopoly-drops-7).
+### Custom Upstream
 
-- **Repository**: A collection of files packaged in a single directory under version control.
+<p>A <dfn id="custom-upstream">custom upstream</dfn> is a repository restricted to members of an organization, containing a common codebase for new sites. This type of repository is a child repository to Pantheon's core upstreams (<a href="https://github.com/pantheon-systems/wordpress">WordPress</a>, <a href="https://github.com/pantheon-upstreams/drupal-composer-managed">Drupal (Latest Version)</a>, <a href="https://github.com/pantheon-systems/drops-7">Drupal 7</a>) and acts as a parent for site level repositories.</p>
 
-- **Remote Repository**: A central version control location, such as a repository residing on GitHub, Bitbucket, or GitLab.
+### Public Upstream
 
-- **Upstream Updates**: Code changes that are made once in a parent (upstream) repository, then applied "downstream" to child repositories. This is how Pantheon's one-click updates work.
+<p>A <dfn id="public-upstream">public upstream</dfn> is a repository that is open to all Pantheon users which contains a common codebase for new sites, like <a href="https://github.com/populist/panopoly-drops-7">Panopoly</a>.</p>
 
-- **Site Repository**: Child repository where upstream updates are applied and site specific customizations are tracked, similar to your site's codebase on Pantheon.
+### Repository
 
+<p>A<dfn id="repository">repository</dfn> is a collection of files packaged in a single directory under version control.</p>
+
+
+### Remote Repository
+
+<p>A <dfn id="remote-repository">remote repository</dfn> is the central version control location, such as a repository residing on GitHub, Bitbucket, or GitLab.</p>
+
+### Upstream Updates
+
+<p><dfn id="upstream-updates"> Upstream Updates</dfn> are code changes that are made once in a parent (upstream) repository, then applied "downstream" to child repositories. This is how Pantheon's one-click updates work.</p>
+
+### Site Repository
+
+<p>A <dfn id="site-repository">site repository</dfn> is a child repository where upstream updates are applied and site specific customizations are tracked, similar to your site's codebase on Pantheon.</p>
+
+### Framework
+
+<p>The <dfn id="framework">framework</dfn> determines the server configuration for a given CMS. It includes things like Nginx configuration, the relevant CLI tool to install (Drush or WP-CLI), etc. This setting is visible to users via Terminus and in the Site Settings. Once a framework has been set, it cannot be changed at the site level through the UI or Terminus. If you need to change your upstream's framework, you would need to contact Support.</p>
 
 ## More Resources