add README

README.md

+To run the stateless core is very easy, just follow the below steps:
+
+### 1. Firstly pull docker images from outer repo 
+
+```
+sudo ./pullimages.sh
+```
+It may take some time, just be patient. Later we will reduce the images size.
+
+### 2. Create a bridge for the containers
+```
+docker network create \
+  --driver=bridge \
+  --subnet=10.244.0.0/16 \
+  -o "com.docker.network.bridge.name"="demo-stateless" \
+  openxg-stateless
+```
+Please modify the IP arrange if your environment is conflict with this.
+
+### 3. Bring up the core network containers
+```
+sudo docker-compose -f docker-stateless.yaml up -d
+```
+It may take some when you start the 5GC compose first time, wait until the mysql container is healthy. But once you run it correctly, it will be very fast.
+
+### 4. Let the balancer 'RISE' know available AMF
+Call the API in RISE, and pass the amf list to it:
+```
+curl -X POST -d '{"amf2":{"ip":"10.244.1.12"}}' http://10.244.1.20:8282/nplugin-dr/v1/create/AmfIpList
+```
+Currently, we only have one AMF. but it can support multiple.
+
+### 5. Bring up the ueransim
+```
+sudo docker run -ti -v $PATH_TO_stateless_etc$:/etc/openxg/ --privileged=true --net=openxg-stateless --ip=10.244.1.21 ubuntu:18.04 /bin/bash
+```
+The gnb and ue config file is mapped to ueransim container /etc/openxg/
+
+run gnb 
+```
+/UERANSIM/build/nr-gnb -c /etc/openxg/gnb.yaml
+```
+connect ue
+```
+/UERANSIM/build/nr-ue -c /etc/openxg/gue.yaml
+```
+Then you will see the virtal interface uesimtun0
+
+### Enjoy
+
+