update readme with docker image instructions

README.md

@@ -2,6 +2,9 @@
 C++ in Embedded Systems, published by Packt 
 
 ## Install and run docker image
+### Pull the image
 `docker pull mahmutbegovic/cpp_in_embedded_systems:latest`
+### Run the image
 `docker run -d -it --name dev_env mahmutbegovic/cpp_in_embedded_systems`
+### Enter bash
 `docker exec -it dev_env /bin/bash`