minor #13814 How to use dev-server with serf-signed domain. (antiseptikk)

This PR was submitted for the 5.1 branch but it was merged into the 3.4 branch instead.

Discussion
----------

How to use dev-server with serf-signed domain.

Adding documentation for --allowed-hosts option to use dev-server with serf-signed domain

Commits
-------

19f3abc How to use dev-server with serf-signed domain.

Author: javiereguiluz

frontend/encore/dev-server.rst

@@ -58,6 +58,21 @@ option:
 
     $ ./node_modules/.bin/encore dev-server --hot
 
+If you want to use SSL with self-signed domain, add 
+the ``--https``, ``--pfx=``, and  ``--allowed-hosts``
+options to the ``dev-server`` command in the ``package.json`` file:
+
+.. code-block:: diff
+
+    {
+        ...
+        "scripts": {
+    -        "dev-server": "encore dev-server",
+    +        "dev-server": "encore dev-server --https --pfx=$HOME/.symfony/certs/default.p12 --allowed-hosts=mydomain.wip",
+            ...
+        }
+    }
+
 If you experience issues related to CORS (Cross Origin Resource Sharing), add
 the ``--disable-host-check`` and ``--port`` options to the ``dev-server``
 command in the ``package.json`` file:
@@ -78,6 +93,7 @@ command in the ``package.json`` file:
     Beware that `it's not recommended to disable host checking`_ in general, but
     here it's required to solve the CORS issue.
 
+
 .. _`webpack-dev-server`: https://webpack.js.org/configuration/dev-server/
 .. _`HMR`: https://webpack.js.org/concepts/hot-module-replacement/
 .. _`it's not recommended to disable host checking`: https://webpack.js.org/configuration/dev-server/#devserverdisablehostcheck