[WebInstallAPI] Add OT update and link to explainer (#1189)

* Add OT update

* remove empty lines

---------

Co-authored-by: Kristin Lee <kristinlee@microsoft.com>

Author: Kbhlee2121

WebInstall/explainer.md

@@ -2,6 +2,10 @@
 Authors: [Diego Gonzalez](https://github.com/diekus)
 
 ## State of the work
+
+>**Here for Origin Trials?** 
+The Web Install API is currently available as an [Origin Trial](https://developer.chrome.com/docs/web-platform/origin-trials/) in Chrome and Microsoft Edge versions 143-148. See [Origin Trial Instructions](https://github.com/MicrosoftEdge/Demos/blob/main/pwa-web-install-api/README.md) to learn more.
+
 The work on Web Install has been separated into two explainers: _current_ and _background_ document installations. The '[**current document**](./explainer-current-doc.md)' installation refers to installation of the curently loaded web application and is [being discussed](https://github.com/w3c/manifest/pull/1175) in the Web Applications WG. The '[**background document**](./explainer-background-doc.md)' installation refers to installation of web applications different from the current loaded navigable. Background document installations are being discussed and incubated in WICG.
 
 | Explainer | Expected Venue |