Add DEVELOPMENT.md and update dev Dockerfile

DEVELOPMENT.md

@@ -0,0 +1,37 @@
+# Development Guide
+
+## Docker local development setup
+
+You should have docker installed in your system, if not click [here](https://docs.docker.com/get-docker/).
+
+1. Go to diagrams root directory.
+
+1. Build the docker image.
+    
+    ```shell
+    docker build --tag diagrams:1.0 -f ./docker/dev/Dockerfile .
+    ```
+    
+1. Create the container, run in background and mount the project source code.
+
+    ```shell
+    docker run -d \
+    -it \
+    --name diagrams \
+    --mount type=bind,source="$(pwd)",target=/usr/src/diagrams \
+    diagrams:1.0
+    ```
+
+1. Run unit tests in the host using the container to confirm that it's working.
+
+    ```shell
+    docker exec diagrams python -m unittest tests/*.py -v
+    ```
+
+1. Run the bash script `autogen.sh` to test.
+
+    ```shell
+    docker exec diagrams ./autogen.sh
+    ```
+
+1. If the unit tests and the bash script `autogen.sh` is working correctly, then your system is now ready for development.

docker/dev/Dockerfile

@@ -18,4 +18,4 @@ WORKDIR /usr/src/diagrams
 COPY . .
 
 # install python requirements.
-RUN pip install -r ./docker/dev/requirements.txt
+RUN pip install black

docker/dev/requirements.txt

@@ -1,2 +0,0 @@
-diagrams
-black