Add dates

Author: smplayer-dev

Release_notes.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## [21.10]
+## [21.10] - 2021-10-??
  * The support for YouTube has been improved by using yt-dlp. Fixes
    buffering and age-restricted videos are supported.
  * Possibility to use yt-dlp instead of youtube-dl.
@@ -15,7 +15,7 @@
 ### Removed
  * Support for the obsolete mplayer2.
 
-## [21.8]
+## [21.8] - 2021-08-16
  * A version for Mac OS is now available.
  * Better automatic resizing of the main window, trying to prevent
    black borders.