docs: add webpush related troubleshooting steps

docs/troubleshooting.mdx

@@ -174,4 +174,36 @@ This can happen if you have a new installation of Jellyfin/Emby or if you have c
 
 This process should restore your admin privileges while preserving your settings.
 
+## Failed to enable web push notifications
+
+### Option 1: You are using Pi-hole
+
+When using Pi-hole, you need to whitelist the proper domains in order for the queries to not be intercepted and blocked by Pi-hole.
+If you are using a chromium based browser (eg: Chrome, Brave, Edge...), the domain you need to whitelist is `fcm.googleapis.com`
+If you are using Firefox, the domain you need to whitelist is `push.services.mozilla.com`
+
+1. Log into your Pi-hole through the admin interface, then click on Domains situated under GROUP MANAGEMENT.
+2. Add the domain corresponding to your browser in the `Domain to be added` field and then click on Add to allowed domains.
+3. Now in order for those changes to be used you need to flush your current dns cache.
+4. You can do so by using this command line in your Pi-hole terminal:
+    ```bash
+    pihole restartdns
+    ```
+If this command fails (which is unlikely), use this equivalent:
+    ```bash
+    pihole -f && pihole restartdns
+    ```
+5. Then restart your Seerr instance and try to enable the web push notifications again.
+
+
+### Option 2: You are using Brave browser
+
+Brave is a "De-Googled" browser. So by default or if you refused a prompt in the past, it cuts the access to the FCM (Firebase Cloud Messaging) service, which is mandatory for the web push notifications on Chromium based browsers.
+
+1. Open Brave and paste this address in the url bar: `brave://settings/privacy`
+2. Look for the option: "Use Google services for push messaging"
+3. Activate this option
+4. Relaunch Brave completely
+5. You should now see the notifications prompt appearing instead of an error message.
+
 If you still encounter issues, please reach out on our support channels.