fix: Mercure env vars (#1487)

Author: dunglas

core/mercure.md

@@ -16,26 +16,9 @@ Then, the Mercure hub dispatches the updates to all connected clients using [Ser
 Mercure support is already installed, configured and enabled in [the API Platform distribution](../distribution/index.md).
 If you use the distribution, you have nothing more to do, and you can skip to the next section.
 
-If you have installed API Platform using another method (such as `composer require api`), you need to install a Mercure hub, and the [Symfony MercureBundle](https://symfony.com/doc/current/mercure.html):
+If you have installed API Platform using another method (such as `composer require api`), you need to install [a Mercure hub](https://mercure.rocks/docs/getting-started) and the Symfony MercureBundle.
 
-First, [download and run a Mercure hub](https://mercure.rocks/docs/hub/install).
-Then, install the Symfony bundle:
-
-```console
-composer require symfony/mercure-bundle
-```
-
-Finally, 3 environment variables [must be set](https://symfony.com/doc/current/configuration.html#configuration-based-on-environment-variables):
-
-* `MERCURE_URL`: the URL that must be used by API Platform to publish updates to your Mercure hub (can be an internal or a public URL)
-* `MERCURE_PUBLIC_URL`: the **public** URL of the Mercure hub that clients will use to subscribe to updates
-* `MERCURE_JWT_SECRET`: a valid Mercure [JSON Web Token (JWT)](https://jwt.io/) allowing API Platform to publish updates to the hub
-
-The JWT **must** contain a `mercure.publish` property containing an array of topic selectors.
-This array can be empty to allow publishing anonymous updates only. It can also be `["*"]` to allow publishing on every topics.
-[Example publisher JWT](https://jwt.io/#debugger-io?token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJtZXJjdXJlIjp7InB1Ymxpc2giOlsiKiJdfX0.obDjwCgqtPuIvwBlTxUEmibbBf0zypKCNzNKP7Op2UM) (demo key: `!ChangeMe!`).
-
-[Learn more about Mercure authorization.](https://mercure.rocks/spec#authorization)
+[Learn how to install and configure MercureBundle manually on the Symfony website](https://symfony.com/doc/current/mercure.html)
 
 ## Pushing the API Updates
 
@@ -72,7 +55,7 @@ Clients generated using [the API Platform Client Generator](../client-generator/
 
 ## Dispatching Private Updates (Authorized Mode)
 
-Mercure allows to dispatch [private updates, that will be received only by authorized clients](https://mercure.rocks/spec#authorization).
+Mercure allows dispatching [private updates, that will be received only by authorized clients](https://mercure.rocks/spec#authorization).
 To receive this kind of updates, the client must hold a JWT containing at least one *target selector* matched by the update.
 
 Then, use options to mark the published updates as privates:
@@ -117,7 +100,7 @@ In addition to `private`, the following options are available:
 
 * `topics`: the list of topics of this update, if not the resource IRI is used
 * `data`: the content of this update, if not set the content will be the serialization of the resource using the default format
-* `id`: the SSE id of this event, if not set the ID will be generated by the mercure Hub
+* `id`: the SSE id of this event, if not set the ID will be generated by the Mercure Hub
 * `type`: the SSE type of this event, if not set this field is omitted
 * `retry`: the `retry` field of the SSE, if not set this field is omitted
 * `normalization_context`: the specific normalization context to use for the update.