Add docker support

Dockerfile

@@ -0,0 +1,5 @@
+FROM python:3.6
+
+ADD requirements.txt /safaribooks/requirements.txt
+WORKDIR /safaribooks
+RUN pip3 install -r requirements.txt

README.md

@@ -38,6 +38,12 @@ It's really simple to use, just choose a book from the library and replace in th
 $ python3 safaribooks.py --cred "account_mail@mail.com:password01" XXXXXXXXXXXXX
 ```
 
+## Usage:
+You can use Docker
+```shell
+$ docker-compose run safaribooks python3 safaribooks.py --cred "account_mail@mail.com:password01" XXXXXXXXXXXXX
+```
+
 The ID is the digits that you find in the URL of the book description page:  
 `https://www.safaribooksonline.com/library/view/book-name/XXXXXXXXXXXXX/`  
 Like: `https://www.safaribooksonline.com/library/view/test-driven-development-with/9781491958698/`  

docker-compose.yml

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+version: '3'
+
+services:
+  safaribooks:
+    build: .
+    volumes:
+       - ./:/safaribooks
+    working_dir: /safaribooks