Update asset_mapper.rst

Adds tip about configuration proxy when connection to jsDelivr is failed

Author: WinterSilence

frontend/asset_mapper.rst

@@ -252,6 +252,25 @@ This adds the ``bootstrap`` package to your ``importmap.php`` file::
     `package.json configuration file`_. Try to contact the package maintainer to
     ask them to fix those issues.
 
+.. tip::
+
+    If you get a error like as ``Connection was reset for "https://cdn.jsdelivr.net/npm/...".``,
+    than you can temporaly configure the proxy for connection to the ``jsDelivr`` CDN:
+
+    .. code-block:: yaml
+
+        # config/packages/framework.yaml
+        framework:
+            # ...
+            http_client:
+                default_options:
+                    proxy: '185.250.180.238:8080'
+                    # If you use CURL, add extra options:
+                    extra:
+                        curl:
+                            # 61 is value of constant CURLOPT_HTTPPROXYTUNNEL
+                            '61': true
+
 Now you can import the ``bootstrap`` package like usual:
 
 .. code-block:: javascript