clarify why someone might want to disable cache_game_state

Author: iCodeSometime

README.md

@@ -181,7 +181,7 @@ Check CHANGELOG.md for details - all breaking changes should be marked as *BREAK
 Some of the improvements made since the fork:
  - Build times are _drastically_ improved. rust-analyzer actually works now (thanks KarelPeeters)
  - Checking the `status` of the `Board` is 2-3x faster for a fully populated board (thanks AlexanderHarrison)
- - Using `Game` is 10-20x faster for reasonably sized games when using the new `cache_game_state` feature (more for larger games)
+ - Using `Game` is 10-20x faster for reasonably sized games when using the new `cache_game_state` feature (more for larger games). If you're in an embedded environment and can't tolerate the extra kb of memory, you can disable this feature.
  - Legality checking of unsanitized moves is 4-5x faster
  - `Game::make_move` now returns `Option<String>` with the SAN representation of the move. `Board::make_move` still returns a bool to avoid overhead in the hot path
  - Optional instrumentation added to `Game`, using [tracing](https://github.com/tokio-rs/tracing) - just use the `instrument_game` feature.