minor update for how_to_build_and_install.md

Signed-off-by: Takeshi Miura <[email protected]>

Author: 1222-takeshi

doc/howto/how_to_build_and_install.md

@@ -39,6 +39,7 @@ if you want to use python API, you need to install python and swig:
 In the YDLidar SDK directory, run the following commands to compile the project:
 ```
 git clone https://github.com/YDLIDAR/YDLidar-SDK.git
+mkdir -p YDLidar-SDK/build
 cd YDLidar-SDK/build
 cmake ..
 make