Add release note for mdn#10334

RELEASE_NOTES.md

@@ -14,6 +14,10 @@ August 19, 2021
 
   We're not ruling out the return of XPath and XSLT data in the future. But for now, in the absence of an intentional effort to create and maintain that data, we thought it best to remove the faulty data. ([#9830](https://github.com/mdn/browser-compat-data/pull/9830))
 
+- The schema now supports a special version value `"preview"` for in-development versions of browsers, such as Safari Technology Preview, Chrome Canary, and Firefox Nightly. Additionally, browser data now supports a `preview_name` property for supplying a corresponding name for the preview browser.
+
+  These additions to the schema should help represent features gated to development versions, which were previously misrepresented with notes, `false` values, or inaccurate version numbers. ([#10334](https://github.com/mdn/browser-compat-data/pull/10334))
+
 - The schema for browser release data now supports the optional `accepts_flags` boolean hint, which indicates whether a browser (or individual release) permits user-configurable preferences. Presently, this is a hint for data contributors or tools. The value of `accepts_flags` doesn't make any guarantees about the contents of feature data. ([#11286](https://github.com/mdn/browser-compat-data/pull/11286))
 
 - Descendant features of `api.HTMLCanvasElement.getContext` and `api.HTMLCanvasElement.toBlob` have been reorganized to follow [the guideline for parameter object features](https://github.com/mdn/browser-compat-data/blob/main/docs/data-guidelines.md#parameters-and-parameter-object-features). See [the PR for a detailed list of features affected](https://github.com/mdn/browser-compat-data/pull/11234#issuecomment-900265901). ([#11234](https://github.com/mdn/browser-compat-data/pull/11234))