update readme to include zlib dependencies

Author: kai-ion

README.md

@@ -50,21 +50,23 @@ AWS SDK for C++ is now in General Availability and recommended for production us
    **_NOTE:_** BUILD_ONLY is an optional flag used to list only the services you are using. Building the whole SDK can take a long time. Also, check out the list of [CMake parameters](./docs/CMake_Parameters.md)
 
 #### Other Dependencies:
-To compile on Linux, you must have the header files for libcurl, libopenssl, and zlib. The packages are typically available in your package manager.
+To compile on Linux, you must have the header files for libcurl, libopenssl. The packages are typically available in your package manager.
 
 Debian based Linux distributions example:
-   `sudo apt-get install libcurl4-openssl-dev libssl-dev zlib1g-dev`
+   `sudo apt-get install libcurl4-openssl-dev libssl-dev`
 
 RPM based Linux distributions example:
-   `sudo [yum|dnf|zypper] install libcurl-devel openssl-devel zlib-devel`
+   `sudo [yum|dnf|zypper] install libcurl-devel openssl-devel`
 
-SUSE example:
-   `sudo zypper install libcurl-devel libopenssl-devel zlib-devel`
+Optional: zlib (for compression)
+zlib is **optional** and only required if you need gzip/deflate compression
+support (for example, when your libcurl and workloads use HTTP content-encoding).
+If your libcurl is already built with zlib, you typically don't need to install
+zlib headers separately unless your build complains about missing zlib.
 
-Arch example:
-   `sudo pacman -S curl openssl zlib`
-
-Why zlib? It's required for HTTP compression/decompression support used by the SDK and its HTTP stack.
+Install if needed:
+- Debian/Ubuntu: `sudo apt-get install zlib1g-dev`
+- RPM-based: `sudo [yum|dnf|zypper] install zlib-devel`
 
 ### Building for MacOS
 
@@ -82,15 +84,6 @@ You must install the [xcode command line tools](https://mac.install.guide/comman
 >  ..
 > ```
 
-zlib on macOS:
-If CMake cannot find zlib, install it with Homebrew and add it to your CMake prefix path:
-```
-brew install zlib
-cmake -DCMAKE_PREFIX_PATH="/opt/homebrew/opt/curl;/opt/homebrew/opt/zlib" \
-      -DZLIB_ROOT=/opt/homebrew/opt/zlib \
-      <other options> ..
-```
-
 ### Building for Android
 To build for Android, add `-DTARGET_ARCH=ANDROID` to your CMake command line. Currently, we support Android APIs from 19 to 28 with Android NDK 19c, and we are using the built-in CMake toolchain file supplied by Android NDK, assuming you have the appropriate environment variables (ANDROID_NDK) set.