Improve docker-compose deployment & documentation

Update image tag for control-panel & nonrtric-gateway

Signed-off-by: ecaiyanlinux <martin.c.yan@est.tech>
Change-Id: I7fbd83dc98896565b82fb5e0813387855ac32007
Issue-ID: NONRTRIC-575
diff --git a/docker-compose/.env b/docker-compose/.env
new file mode 100644
index 0000000..6c9743b
--- /dev/null
+++ b/docker-compose/.env
@@ -0,0 +1,24 @@
+#  ============LICENSE_START===============================================
+#  Copyright (C) 2021 Nordix Foundation. All rights reserved.
+#  ========================================================================
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#  ============LICENSE_END=================================================
+#
+
+#CONTROL_PANEL
+CONTROL_PANEL_IMAGE_BASE="nexus3.o-ran-sc.org:10004/o-ran-sc/nonrtric-controlpanel"
+CONTROL_PANEL_IMAGE_TAG="2.3.0"
+
+#NONRTRIC_GATEWAY
+NONRTRIC_GATEWAY_IMAGE_BASE="nexus3.o-ran-sc.org:10004/o-ran-sc/nonrtric-gateway"
+NONRTRIC_GATEWAY_IMAGE_TAG="1.1.0"
\ No newline at end of file
diff --git a/docker-compose/README.md b/docker-compose/README.md
index 6a66c0e..d7542a8 100644
--- a/docker-compose/README.md
+++ b/docker-compose/README.md
@@ -1,4 +1,5 @@
-## License
+# License
+
 Copyright (C) 2020 Nordix Foundation.
 Licensed under the Apache License, Version 2.0 (the "License")
 you may not use this file except in compliance with the License.
@@ -14,11 +15,21 @@
 
 For more information about license please see the [LICENSE](LICENSE.txt) file for details.
 
-## O-RAN-SC docker-compose files:
+## O-RAN-SC docker-compose files
+
 The docker compose file helps the user to deploy the components of nonrtric control panel with one command.
 
+NOTE:
+docker image urls & tags are in file ```.env```
+
 To install the Control Panel and gateway, run the following command:
-docker-compose -f docker-compose.yaml -f control-panel/docker-compose.yaml -f nonrtric-gateway/docker-compose.yaml up -d
+
+```shell
+docker-compose --env-file .env -f docker-compose.yaml -f control-panel/docker-compose.yaml -f nonrtric-gateway/docker-compose.yaml up -d
+```
 
 To remove the containers, use the command:
-docker-compose -f docker-compose.yaml -f control-panel/docker-compose.yaml -f nonrtric-gateway/docker-compose.yaml down
+
+```shell
+docker-compose --env-file .env -f docker-compose.yaml -f control-panel/docker-compose.yaml -f nonrtric-gateway/docker-compose.yaml down
+```
diff --git a/docker-compose/control-panel/docker-compose.yaml b/docker-compose/control-panel/docker-compose.yaml
index bc56c3d..2716ed8 100644
--- a/docker-compose/control-panel/docker-compose.yaml
+++ b/docker-compose/control-panel/docker-compose.yaml
@@ -22,7 +22,7 @@
 
 services:
   policy-control-panel:
-    image: nexus3.o-ran-sc.org:10004/o-ran-sc/nonrtric-controlpanel:2.2.0
+    image: "${CONTROL_PANEL_IMAGE_BASE}:${CONTROL_PANEL_IMAGE_TAG}"
     container_name: policy-control-panel
     networks:
       - default
diff --git a/docker-compose/nonrtric-gateway/docker-compose.yaml b/docker-compose/nonrtric-gateway/docker-compose.yaml
index f2bcdce..fbf3d9b 100644
--- a/docker-compose/nonrtric-gateway/docker-compose.yaml
+++ b/docker-compose/nonrtric-gateway/docker-compose.yaml
@@ -22,7 +22,7 @@
 
 services:
   nonrtric-gateway:
-    image: nexus3.o-ran-sc.org:10004/o-ran-sc/nonrtric-gateway:1.0.0
+    image: "${NONRTRIC_GATEWAY_IMAGE_BASE}:${NONRTRIC_GATEWAY_IMAGE_TAG}"
     container_name: nonrtric-gateway
     networks:
       default: