update readme.md for all samples

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/nginx-flask-mongo/README.md

@@ -0,0 +1,71 @@
+## Compose sample application
+### Python/Flask application with Nginx proxy and a Mongo database
+
+Project structure:
+```
+.
+├── docker-compose.yaml
+├── flask
+│   ├── Dockerfile
+│   ├── requirements.txt
+│   └── server.py
+└── nginx
+    └── nginx.conf
+
+```
+
+[_docker-compose.yaml_](docker-compose.yaml)
+```
+services:
+  web:
+    build: app
+    ports:
+    - 80:80
+  backend:
+    build: flask
+    ...
+  mongo:
+    image: mongo
+```
+The compose file defines an application with three services `web`, `backend` and `db`.
+When deploying the application, docker-compose maps port 80 of the web service container to port 80 of the host as specified in the file.
+Make sure port 80 on the host is not being used by another container, otherwise the port should be changed.
+
+## Deploy with docker-compose
+
+```
+$ docker-compose up -d
+Creating network "nginx-flask-mongo_default" with the default driver
+Pulling mongo (mongo:)...
+latest: Pulling from library/mongo
+423ae2b273f4: Pull complete
+...
+...
+Status: Downloaded newer image for nginx:latest
+Creating nginx-flask-mongo_mongo_1 ... done
+Creating nginx-flask-mongo_backend_1 ... done
+Creating nginx-flask-mongo_web_1     ... done
+
+```
+
+## Expected result
+
+Listing containers must show two containers running and the port mapping as below:
+```
+$ docker ps
+CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
+a0f4ebe686ff        nginx                       "/bin/bash -c 'envsu…"   About a minute ago   Up About a minute   0.0.0.0:8080->80/tcp   nginx-flask-mongo_web_1
+dba87a080821        nginx-flask-mongo_backend   "./server.py"            About a minute ago   Up About a minute                          nginx-flask-mongo_backend_1
+d7eea5481c77        mongo                       "docker-entrypoint.s…"   About a minute ago   Up About a minute   27017/tcp              nginx-flask-mongo_mongo_1
+```
+
+After the application starts, navigate to `http://localhost:80` in your web browser or run:
+```
+$ curl localhost:80
+Hello fom the MongoDB client!
+```
+
+Stop and remove the containers
+```
+$ docker-compose down
+```