docs: add example Dockerfile (#924)

(cherry picked from commit 1a751dd)

Author: kingsodigie

docker/Dockerfile

@@ -0,0 +1,5 @@
+# Import Node base image (change version as needed)
+FROM node:12-slim
+
+#Install the node SDK
+RUN npm install ibm-watson

docker/README.md

@@ -0,0 +1,23 @@
+## Docker
+You can use docker to test issues you have with the SDK.
+
+1.  Install docker
+    -   Mac: <https://docs.docker.com/docker-for-mac/install/>
+    -   Windows: <https://docs.docker.com/docker-for-windows/install/>
+
+2.  Download the dockerfile for this SDK and edit as needed.
+    -   Change the node version as needed `FROM node:<your-version>`
+        -   For valid node base images on docker see <https://hub.docker.com/_/node>
+
+    -   Copy code/file that you wish to test into the dockerfile 
+        -   Add line `COPY <src>... <dest>`
+
+    -   Set dockerfile to execute code file 
+        -   Add line `CMD [ "<executable>" ]`
+    
+    -   For more information on dockerfile construction please visit <https://docs.docker.com/engine/reference/builder/>
+
+3.  Build and run the docker image.
+    -   Navigate to docker file directory
+    -   To build the docker image run `docker build --tag=<your-tag> .`
+    -   To run the docker image run `docker run <your-tag>`