fix(NcRichContenteditable): make the default placeholder short

Signed-off-by: Grigorii K. Shartsev <me@shgk.me>

src/components/NcRichContenteditable/NcRichContenteditable.vue

@@ -201,7 +201,7 @@ export default {
 
 		placeholder: {
 			type: String,
-			default: t('Write message, use "@" to mention someone, use ":" for emoji autocompletion …'),
+			default: t('"@" to mention, ":" for emoji …'),
 		},
 
 		autoComplete: {