Improve simple demo for multi-nodes with README and minor changes (#201) (#202)

Co-authored-by: Louie Tsai <louie.tsai@intel.com>

Author: zhangxiaoli73

demo/README.md

@@ -0,0 +1,34 @@
+# Simple Demo for Intel® oneCCL Bindings for PyTorch*
+
+This simple demo show case the functionality for collective communication primitives in Intel® oneCCL Bindings for PyTorch*.
+
+## Single Node Run
+To run the simple demo on a single node with 2 instances, run: 
+
+```bash
+mpirun -n 2 -l python demo.py
+
+```
+The demo could be also run on XPU with " --device xpu " argument. 
+
+```bash
+mpirun -n 2 -l python demo.py --device xpu
+```
+
+## Multiple Nodes Run
+To run the simple demo on multiple nodes, please follow below instructions:
+
+### Ethernet
+1. Identify the network interface name for collective communication. ex: eth0
+2. Identify the IPs of all nodes. ex: 10.0.0.1,10.0.0.2
+3. Identify the master node IP. ex: 10.0.0.1
+4. Set the value of np for the total number of instances. ex: 2
+5. Set the value of ppn for the number of instance per node. ex: 1
+
+Here is a run command example for cpu according to above steps:
+
+```bash
+FI_TCP_IFACE=eth0 I_MPI_OFI_PROVIDER=tcp I_MPI_HYDRA_IFACE=eth0  I_MPI_DEBUG=121 mpirun -host 10.0.0.1,10.0.0.2 -np 2 -ppn 1  --map-by node  python demo.py --device cpu --dist_url 10.0.0.1  --dist_port 29500
+```
+The demo could be also run on XPU by changing " --device cpu " to " --device xpu " argument. 
+