Modify cmake instruction in build from source (#1445)

README.md

@@ -81,7 +81,7 @@ $ git submodule update --init --recursive --depth=1
 ```
 You may substitute an installation path of your own choosing by passing `CMAKE_INSTALL_PREFIX`. For example:
 ```shell
-$ cmake -DCMAKE_INSTALL_PREFIX=$PWD/rccl-install ..
+$ cmake -DCMAKE_INSTALL_PREFIX=$PWD/rccl-install -DCMAKE_BUILD_TYPE=Release ..
 ```
 Note: ensure rocm-cmake is installed, `apt install rocm-cmake`.
 

docs/install/building-installing.rst

@@ -45,11 +45,12 @@ to ``CMAKE_INSTALL_PREFIX``, for example:
 
 .. code-block:: shell
 
-    cmake -DCMAKE_INSTALL_PREFIX=$PWD/rccl-install ..
+    cmake -DCMAKE_INSTALL_PREFIX=$PWD/rccl-install -DCMAKE_BUILD_TYPE=Release ..
 
 .. note::
 
-    Ensure ROCm CMake is installed using the command ``apt install rocm-cmake``.
+    Ensure ROCm CMake is installed using the command ``apt install rocm-cmake``. By default,
+    CMake builds the component in debug mode unless ``DCMAKE_BUILD_TYPE`` is specified.
 
 
 Building the RCCL package and install package: