[Encore] Adding more FAQs for #8072

Author: weaverryan

Diff for: frontend.rst

@@ -64,7 +64,7 @@ Guides
 Troubleshooting
 ...............
 
-* :doc:`FAQ </frontend/encore/faq>`
+* :doc:`FAQ & Common Issues </frontend/encore/faq>`
 
 Full API
 ........

Diff for: frontend/encore/faq.rst

@@ -1,14 +1,11 @@
-Frequently Asked Questions
-==========================
+FAQ and Common Issues
+=====================
 
 My App Lives under a Subdirectory
 ---------------------------------
 
-    My app doesn't live at the root of my web server: it lives under a subdirectory
-    (e.g. ``/myAppSubdir/``). How can I configure Encore to work?
-
-If your app lives under a subdirectory, you just need to include that when calling
-``Encore.setPublicPrefix()``:
+If your app does not live at the root of your web server (i.e. it lives under a subdirectory,
+like ``/myAppSubdir``), you just need to configure that when calling ``Encore.setPublicPrefix()``:
 
 .. code-block:: diff
 
@@ -37,3 +34,20 @@ final paths:
         "build/app.js": "/myAppSubdir/build/app.123abc.js",
         "build/dashboard.css": "/myAppSubdir/build/dashboard.a4bf2d.css"
     }
+
+"jQuery is not defined" or "$ is not defined"
+---------------------------------------------
+
+This error happens when your code (or some library that you are using) expects ``$``
+or ``jQuery`` to be a global variable. But, when you use Webpack and ``require('jquery')``,
+no global variables are set.
+
+The fix depends on if the error is happening in your code or inside some third-party
+code that you're using. See :doc:`/frontend/encore/legacy-apps` for the fix.
+
+Uncaught ReferenceError: webpackJsonp is not defined
+----------------------------------------------------
+
+If you get this error, it's probably because you've just added a :doc:`shared entry </frontend/encore/shared-entry>`
+but you *forgot* to add a ``script`` tag for the new ``manifest.js`` file. See the
+information about the :ref:`script tags <encore-shared-entry-script>` in that section.

Diff for: frontend/encore/shared-entry.rst

@@ -27,6 +27,8 @@ that's included on every page:
 As soon as you make this change, you need to include two extra JavaScript files
 on your page before any other JavaScript file:
 
+.. _encore-shared-entry-script:
+
 .. code-block:: twig
 
     <!-- these two files now must be included in every page -->