[=] add guidance for building on MacOS, update dingtalk group image.

README.md

@@ -65,7 +65,7 @@ To run test cases, you need
 
 ## QuickStart Guide
 
-XQUIC supports both BabaSSL and BoringSSL.
+XQUIC can be built with Tongsuo(BabaSSL) or BoringSSL.
 
 ### Build with BoringSSL
 
@@ -86,6 +86,7 @@ SSL_PATH_STR="${PWD}"
 SSL_INC_PATH_STR="${PWD}/include"
 SSL_LIB_PATH_STR="${PWD}/build/ssl/libssl.a;${PWD}/build/crypto/libcrypto.a"
 cd ../..
+## Note: if you don’t have golang in your environment, please install [golang](https://go.dev/doc/install) first. 
 
 # build XQUIC with BoringSSL
 git submodule update --init --recursive
@@ -160,4 +161,4 @@ Feel free to contact us in the following ways:
 * Dingtalk group: 34059705
 * slack channel: #xquic in quicdev group
 
-  <img src="docs/images/dingtalk_group.jpg" width=200 alt="dingtalk group"/>
+  <img src="docs/images/dingtalk_group.png" width=200 alt="dingtalk group"/>

docs/Platforms.md

@@ -35,20 +35,29 @@ make -j
 
 You can use the cmake variables `-DPLATFORM=mac` to build XQUIC on macOS.
 
+Remember you still need to install BoringSSL or Tongsuo(BabaSSL) first, please follow to the guidance [get and build BoringSSL](https://github.com/alibaba/xquic#build-with-boringssl) / [get and build BabaSSL](https://github.com/alibaba/xquic#build-with-babassl).
+
 ```bash
-# build XQUIC with BabaSSL
+
+# build XQUIC with BoringSSL
+
 git submodule update --init --recursive
 mkdir build; cd build
-cmake -DPLATFORM=mac ..
+cmake -DPLATFORM=mac -DSSL_TYPE=${SSL_TYPE_STR} -DSSL_PATH=${SSL_PATH_STR} -DSSL_INC_PATH=${SSL_INC_PATH_STR} -DSSL_LIB_PATH=${SSL_LIB_PATH_STR} -DXQC_SUPPORT_SENDMMSG_BUILD=0 ..
 make -j
 
-# build XQUIC with BoringSSL
+
+# build XQUIC with BabaSSL
 git submodule update --init --recursive
 mkdir build; cd build
-cmake -DPLATFORM=mac -DSSL_TYPE=${SSL_TYPE_STR} -DSSL_PATH=${SSL_PATH_STR} -DSSL_INC_PATH=${SSL_INC_PATH_STR} -DSSL_LIB_PATH=${SSL_LIB_PATH_STR} ..
+cmake -DPLATFORM=mac -DXQC_SUPPORT_SENDMMSG_BUILD=0 ..
 make -j
+
 ```
 
+Troubleshooting:
+> Note: sendmmsg is not supported on MacOS, make sure you add -DXQC\_SUPPORT\_SENDMMSG\_BUILD=0 to turn off the feature 
+
 ## Windows Release
 
 ```bash