Add dockerfile description, fix permission problem

Signed-off-by: eyuen <eyuen@redhat.com>

Author: elsony

docker/Dockerfile

@@ -1,8 +1,23 @@
+####
+# This Dockerfile is used in order to build a container that runs the Spring Boot application
+#
+# Build the image with:
+#
+# docker build -f docker/Dockerfile -t python/sample-basic .
+#
+# Then run the container using:
+#
+# docker run -i --rm -p 8080:8080 python/sample-basic
+####
 FROM python:slim
 
 WORKDIR /projects
 COPY . .
-RUN pip install --user -r requirements.txt
+
+RUN python3 -m venv venv
+RUN . venv/bin/activate
+RUN pip install -r requirements.txt
 
 EXPOSE 8080
-CMD [ "python", "app.py" ]
+CMD [ "python", "app.py"]
+