iSulad: add python3 and device mapper into Dockerfile

Signed-off-by: NLiFeng <lifeng68@huawei.com>

Dockerfile

@@ -63,8 +63,11 @@ RUN yum clean all && yum swap -y fakesystemd systemd && \
 			gmock \
 			gmock-devel \
 			cppcheck \
+			python3 \
+			python3-pip \
 			python \
 			python-pip \
+			device-mapper-devel \
 			libcurl-devel \
 			zlib-devel \
 			glibc-headers \

docs/build_guide.md

@@ -23,7 +23,9 @@ $ sudo make
 $ sudo make install
 ```
 
-## Via Docker container
+## Trial iSulad Via Docker container
+
+You can try to use iSulad via Docker container. The following steps guide you how to create a Docker container which can run iSulad inside.
 
 #### Build image
 
@@ -45,12 +47,12 @@ $ sudo mkdir -p /var/lib/isulad
 
 #### Build iSulad in container
 
-Let's suppose that you built an image called `iSulad:dev`.
+Let's suppose that you built an image called `isulad:dev`.
 
 Then from the iSulad source root directory you can run the following command:
 
 ```sh
-$ sudo docker run -tid --name YOUR_CONTAINER_NAME -v /var/lib/isulad:/var/lib/isulad -v `pwd`:/src/isulad --privileged iSulad:dev
+$ sudo docker run -tid --name YOUR_CONTAINER_NAME -v /var/lib/isulad:/var/lib/isulad -v `pwd`:/src/isulad --privileged isulad:dev
 ```
 
 Let's suppose that you run an container named `iSulad_build`. Then you can use the following commands to build iSulad in your container `iSulad_build`: