Fix variable name in Linux build instructions

0b41a1b (CMake: expose BUILD_TESTNG option, rename LOGGER to
ENABLE_LOGGER, 2024-04-29) had originally introduced this change. It
looks like d132a1c (Merge pull request #251 from
winterheart/pstring-unittests, 2024-05-01) unintentionally removed this
change.

Author: Jayman2000

README.md

@@ -52,15 +52,15 @@ cmake --build --preset mac --config [Debug|Release]
 ```sh
 sudo apt update
 sudo apt install -y --no-install-recommends ninja-build cmake g++ libsdl1.2-dev libsdl-image1.2-dev libncurses-dev zlib1g-dev libspdlog-dev
-cmake --preset linux -D LOGGER=[ON|OFF]
+cmake --preset linux -D ENABLE_LOGGER=[ON|OFF]
 cmake --build --preset linux --config [Debug|Release]
 ```
 
 #### Building - Linux (Fedora)
 ```sh
 sudo dnf update --refresh
 sudo dnf install -y ninja-build cmake gcc-c++ SDL-devel SDL_image-devel ncurses-devel zlib-devel spdlog-devel
-cmake --preset linux -D LOGGER=[ON|OFF]
+cmake --preset linux -D ENABLE_LOGGER=[ON|OFF]
 cmake --build --preset linux --config [Debug|Release]
 ```