changed 'the_end' to '999_the_end'

exercises/999_the_end.zig

@@ -0,0 +1,8 @@
+// This is the end for now!
+// More exercises will follow...
+
+const print = @import("std").debug.print;
+
+pub fn main() void {
+    print("\nThis is the end for now!\nWe hope you had fun and were able to learn a lot, so visit us again when the next exercises are available.\n", .{});
+}