Document zlib-ng compat mode as optional optimization

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bmehta001

docs/building-with-vcpkg.md

@@ -110,6 +110,35 @@ Windows, macOS/iOS, and Android use platform-native HTTP clients (WinInet,
 NSURLSession, and HttpClient_Android respectively), so curl is not required
 on those platforms.
 
+## Optional: SIMD-Optimized zlib with zlib-ng
+
+The vcpkg port depends on stock `zlib` by default. If you want SIMD-optimized
+compression (Intel PCLMULQDQ/AVX2, ARM NEON, etc.), you can transparently
+replace zlib with [zlib-ng](https://github.com/zlib-ng/zlib-ng) in
+compatibility mode. No changes to the port or SDK code are needed.
+
+**Add one line to your vcpkg triplet file** (e.g., `x64-windows-static.cmake`):
+
+```cmake
+set(ZLIB_COMPAT ON)
+```
+
+Then install `zlib-ng` instead of `zlib`:
+
+```console
+vcpkg install zlib-ng mstelemetry --triplet=x64-windows-static
+```
+
+With `ZLIB_COMPAT=ON`, zlib-ng installs as a drop-in replacement — it provides
+the same `zlib.h` header, the same function names (`deflate`, `inflate`,
+`crc32`), and the same `ZLIB::ZLIB` CMake target. All packages that depend on
+`zlib` (including `mstelemetry` and any other libraries like `onnxruntime`)
+will automatically use the optimized zlib-ng build.
+
+> **Important:** All libraries in the same binary should link against the same
+> zlib. When using `ZLIB_COMPAT=ON`, ensure all dependencies resolve to
+> zlib-ng rather than mixing stock zlib and zlib-ng.
+
 ## How It Works: MATSDK_USE_VCPKG_DEPS
 
 When the SDK detects it is being built via vcpkg (by checking for