update readme

Author: dclong

readme.md

@@ -17,6 +17,7 @@ and mounts the current working directory and `/home` on the host machine
 to `/workdir` and `/home_host` in the container respectively.
 ```
 docker run -d --init \
+    --platform linux/amd64 \
     --hostname jupyterhub-pytorch \
     --log-opt max-size=50m \
     -p 8000:8000 \
@@ -33,6 +34,7 @@ The following command (only works on Linux) does the same as the above one
 except that it limits the use of CPU and memory.
 ```
 docker run -d --init \
+    --platform linux/amd64 \
     --hostname jupyterhub-pytorch \
     --log-opt max-size=50m \
     --memory=$(($(head -n 1 /proc/meminfo | awk '{print $2}') * 4 / 5))k \