[Glitch] Add reminder when about to post without alt text in web UI

Port 1e70da5e3c to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/actions/compose.js

@@ -192,6 +192,9 @@ export function directCompose(account) {
   };
 }
 
+/**
+ * @param {null | string} overridePrivacy
+ */
 export function submitCompose(overridePrivacy = null) {
   return function (dispatch, getState) {
     let status     = getState().getIn(['compose', 'text'], '');