Document hideNavigation app portal query param (#256)

And also update docs for `next`. It now supports all pages.

Author: svix-lucho

docs/app-portal.mdx

@@ -208,7 +208,7 @@ If you want your users to be redirected to a specific page of the App Portal, yo
 https://app.svix.com/login?next=/endpoints/abc#key=xyz
 ```
 
-You should use a URL parsing library to add the query parameter (avoid editing the URL manually). Not all pages are supported.
+You should use a URL parsing library to add the query parameter (avoid editing the URL manually).
 
 ### Feature flags
 
@@ -318,6 +318,7 @@ The supported parameters are:
 - `icon` - a URL to an image file. E.g. `https://www.example.com/logo.png` (remember to URL-encode it!).
 - `fontFamily` - one of the fonts listed in the dashboard (see previous section). E.g. `Roboto`.
 - `darkMode` - when set to `true`, dark mode will be turned on by default when the app portal is opened.
+- `hideNavigation` - when set to `true`, the navigation tabs will be hidden. This can be useful to embed only specific sections of the app portal, in combination with the `next` parameter (see [Showing a specific page](#showing-a-specific-page)).
 - `noGutters` - when set to `true`, the app portal will not have any left or right padding within the iframe. This can be useful to align the app portal content with other elements in your site.
 
 So for example: