Update newPage to reflect 1-to-1 change

The description on browser.newPage needs to reflect the new change
where only one browserContext can be open at any given time per
browser. We need to notify the user how they can work with this new
behaviour.

Author: ankur22

src/data/markdown/docs/02 javascript api/07 k6-experimental/01 browser/newpage--options--.md

@@ -3,7 +3,13 @@ title: 'newPage([options])'
 excerpt: 'Browser module: newPage method'
 ---
 
-Creates a new [Page](/javascript-api/k6-experimental/browser/page/) in a new [BrowserContext](/javascript-api/k6-experimental/browser/browsercontext/) and returns the page. You do not need to create a new `BrowserContext` prior to using `newPage`.
+Creates and returns a new [Page](/javascript-api/k6-experimental/browser/page/) in a new [BrowserContext](/javascript-api/k6-experimental/browser/browsercontext/) if a `BrowserContext` hasn't already been initialized for the [Browser](/javascript-api/k6-experimental/browser). If a `BrowserContext` has already been initialized an error is thrown.
+
+<Blockquote mod="note" title="">
+
+A 1-to-1 mapping between [Browser](/javascript-api/k6-experimental/browser) and `BrowserContext` means you cannot run `BrowserContexts` concurrently. Due to this restriction, if one already exists, it must be [retrieved](/javascript-api/k6-experimental/browser/context) and [close](/javascript-api/k6-experimental/browser/browsercontext/close)d first before creating a new one.
+
+</Blockquote>
 
 <TableWithNestedRows>