doc: add changelog to readme

Author: kdxcxs

README.md

@@ -63,3 +63,4 @@ All other information should be explored by reading the source code!
 - [2023/3/21 22:00] feat: support getting hero's candidate id.([#21](https://github.com/Escapingbug/dotaxctf/pull/21))
 - [2023/3/23 13:30] fix: remove non-hero units after round ends.([#23](https://github.com/Escapingbug/dotaxctf/pull/23), reporter: AAA剑圣)
 - [2023/3/24 00:22] feat: support `GetItemInSlot(slot)` to return a sandboxed item.([#24](https://github.com/Escapingbug/dotaxctf/pull/24), reporter: AAA剑圣)
+- [2023/3/27 00:22] feat: support getting game time by `GetGameTime()`.([#28](https://github.com/Escapingbug/dotaxctf/pull/28), reporter: Syclover)