Add tech notes

src/components/block-editor-contents/use-yjs.js

@@ -46,6 +46,7 @@ function initYDoc( { initialBlocks, onRemoteDataChange, channelId, transport } )
 		debug( `connected (channelId: ${ channelId })` );
 
 		if ( isFirstInChannel ) {
+			debug( 'first in channel' );
 			doc.startSharing( { title: '', initialBlocks } );
 		} else {
 			doc.connect();

src/stories/collab/Collaboration.stories.tsx

@@ -17,6 +17,18 @@ const Template: Story< Props > = ( args ) => {
 		<>
 			<p>Open this page in another window to test real time collaborative editing.</p>
 			<IsolatedBlockEditor { ...args } />
+			<p>
+				This local demo depends on shared Local Storage (instead of network) to pass messages across tabs. It
+				will not work:
+			</p>
+			<ul>
+				<li>across browsers</li>
+				<li>across private browsing windows</li>
+				<li>
+					in Safari, until the fix to <a href="https://bugs.webkit.org/show_bug.cgi?id=225344">this bug</a>{ ' ' }
+					has shipped
+				</li>
+			</ul>
 		</>
 	);
 };