Specify description format as markdown

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

app/soapbox/actions/events.ts

@@ -249,6 +249,7 @@ const submitEvent = () =>
       status,
       start_time: startTime,
       join_mode: joinMode,
+      content_type: 'text/markdown',
     };
 
     if (endTime)  params.end_time    = endTime;

app/soapbox/features/event/event-information.tsx

@@ -1,6 +1,7 @@
 import React, { useCallback, useEffect, useState } from 'react';
 import { FormattedDate, FormattedMessage } from 'react-intl';
 
+import { openModal } from 'soapbox/actions/modals';
 import { fetchStatus } from 'soapbox/actions/statuses';
 import MissingIndicator from 'soapbox/components/missing-indicator';
 import StatusContent from 'soapbox/components/status-content';