Add missing documentation for BGWORKER_BYPASS_ALLOWCONN

This was missed in eed1ce72.

Reported by Michael Paquier

doc/src/sgml/bgworker.sgml

@@ -189,15 +189,17 @@ typedef struct BackgroundWorker
   </para>
 
   <para>Once running, the process can connect to a database by calling
-   <function>BackgroundWorkerInitializeConnection(<parameter>char *dbname</parameter>, <parameter>char *username</parameter>)</function> or
-   <function>BackgroundWorkerInitializeConnectionByOid(<parameter>Oid dboid</parameter>, <parameter>Oid useroid</parameter>)</function>.
+   <function>BackgroundWorkerInitializeConnection(<parameter>char *dbname</parameter>, <parameter>char *username</parameter>, <parameter>uint32 flags</parameter>)</function> or
+   <function>BackgroundWorkerInitializeConnectionByOid(<parameter>Oid dboid</parameter>, <parameter>Oid useroid</parameter>, <parameter>uint32 flags</parameter>)</function>.
    This allows the process to run transactions and queries using the
    <literal>SPI</literal> interface.  If <varname>dbname</varname> is NULL or
    <varname>dboid</varname> is <literal>InvalidOid</literal>, the session is not connected
    to any particular database, but shared catalogs can be accessed.
    If <varname>username</varname> is NULL or <varname>useroid</varname> is
    <literal>InvalidOid</literal>, the process will run as the superuser created
-   during <command>initdb</command>.
+   during <command>initdb</command>. If <literal>BGWORKER_BYPASS_ALLOWCONN</literal>
+   is specified as <varname>flags</varname> it is possible to bypass the restriction
+   to connect to databases not allowing user connections.
    A background worker can only call one of these two functions, and only
    once.  It is not possible to switch databases.
   </para>