chore: fix link to incubation repo

Author: marcoscaceres

index.html

@@ -2791,7 +2791,7 @@ <h2>
           <a href="https://github.com/w3c/manifest/pull/836">removed from the
           specification</a> because they did not have support from two or more
           implementers. You can now find them in the <a href=
-          "https://github.com/WICG/beforeinstallprompt">`BeforeInstallPrompt`
+          "https://github.com/WICG/manifest-incubations">`BeforeInstallPrompt`
           event and `window.onappinstalled` repository</a> at the <a href=
           "https://wicg.io"><abbr title=
           "Web Incubator Community Group">WICG</abbr></a>.