Update manual.md

(Happy new year!)

manual.md

@@ -105,4 +105,4 @@ In addition to its shuffle, it brings forth several other unique mechanics not a
 * The minimum difficulty rises as more levels are cleared. If the starting difficulty becomes less than this threshold, then it will increase accordingly. A maximum difficulty of 6.5 (Hard) can be reached this way, achieved by reaching level 43. (If the starting difficulty is already at least this high, then this mechanic is ineffective.)
 * Since the objective is to simply score as high as possible, no continues are allowed throughout the campaign. If the available lives are exhausted, then the game simply ends on the spot.
 
-*Nebunoid (C) 2023 Paul Ruediger. Nebulae artwork courtesy of NASA, ESA, and/or other astrophysical observatories and stations. Please check the [credits](credits.md) for more details.*
+*Nebunoid (C) 2023-2024 Paul Ruediger. Nebulae artwork courtesy of NASA, ESA, and/or other astrophysical observatories and stations. Please check the [credits](credits.md) for more details.*