Add Open edX support doc for enabling waffle flags

source/site_ops/how-tos/add-waffle-flag-for-user.rst

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+How to Enable a Waffle Flag for a User
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+
+Follow these steps to enable a waffle flag for a single user. This may be useful in certain situations, such as internal testing or limited releases:
+
+#. Get the LMS User ID, via a database query or other methods if you have them.
+#. Login to the appropriate Django Admin Portal.
+#. Navigate to ``DJANGO-WAFFLE > Flags``.
+#. Find and select the appropriate flag using the `Open edX Feature Toggles Guide <https://docs.openedx.org/projects/edx-platform/en/latest/references/featuretoggles.html.>`_
+#. Set the ``Everyone`` dropdown to ``Unknown``. This will cause the criterion specified on the page to be evaluated. Setting ``Everyone`` to ``True`` or ``False`` applies the flag globally.
+#. Add the LMS User ID from Step 1 to the ``Users`` textbox at the bottom of the page. To add multiple users, values should be comma-separated with no spaces.
+#. Click the appropriate ``Save`` button.
+#. Refresh the page and see that the entered LMS User ID(s) now correspond to their LMS Usernames.