Adding instructions to create and use custom image with container UI.

doc/rtvsd/rtvs-docker-container.md

@@ -32,3 +32,24 @@ RTVS client v1.3 onwards supports working with docker containers. Please install
 2. You can connect to any container listed here by double clicking or clicking on the connect button.
 
 ![Workspaces window and REPL window in R Tools for Visual Studio (VS2017)](media/workspaces-window-container-connected.png)
+
+## Using custom built images
+
+RTVS Container feature will detect and allow management of containers created using custom built images. Here is a sample docker image built using microsoft/rtvs image. The base image used below has rtvs-daemon, R 3.4.2, and common R packages pre-installed. Change the **username** and **password** in the Dockerfile below as needed.
+
+```
+FROM microsoft/rtvs:1.3-ub1604-r3.4.2
+RUN useradd --create-home ruser1
+RUN echo "ruser1:foobar" | chpasswd
+```
+
+Note the username and password. Build the image using following commands. Change the container **name** as needed:
+
+```
+docker build -t my-rtvs-image:latest .
+docker run -p 6056:5444 --name my-rtvs-container my-rtvs-image:latest rtvsd
+```
+
+In the `docker run` command, we used port 6056 to map to internal port 5444. RTVS uses this to detect rtvs-daemon. Any container which uses exposes container port 5444 will be listed in the RTVS Container UI. You can now connect to `my-rtvs-container` from the workspaces window. You will need to use `<<unix>>\ruser1` as the username while connecting.
+
+![Remote Logon Window](media/remote-logon-window.png)