Write docs for setting up and running MWS (basics).

[roadsideseb]

As pointed out by @natea in #4, #5 and #6, running the sandbox is not documented and not easy to achieve without instruction. This needs to be fixed. Also some instruction on how to run tests are required.

• Update the README.rst with some basic documentation
• Describe setting up and running the sandbox
• Document the basics for developers such as running tests.

[natea]

I would suggest improving the "Getting started" documentation page (https://github.com/tangentlabs/django-oscar-mws/blob/master/docs/source/getting_started.rst) as it doesn't really explain how to get started.

I found that I had to fumble around in the "Amazon MWS" dashboard area to figure out how to connect my Django Oscar site to my Amazon MWS account.

1. Add a merchant account here (http://localhost:8000/en-us/dashboard/merchants/). Need AWS API key, AWS API secret and Seller/Merchant ID, which you can get by registering for a MWS account here: https://developer.amazonservices.com/gp/mws/registration/register.html
2. Update the merchant's marketplaces by choosing "Update marketplaces" from the Actions menu (not sure if this is necessary).
3. From the MWS profile management screen (called "Profiles" in the menu), for each product that you want to sell via Amazon, choose "Create Amazon profile" from the Actions menu. (I'm not sure why the SKU field is empty when I entered a SKU when I created the product in Oscar). Be sure to choose "Fulfillment by Amazon" if Amazon is shipping and handling the product.
4. From the MWS profile management screen (called "Profiles" in the menu), choose "Create new products" from the submission selection menu and submit. This will check if the SKU number in your Oscar store matches the SKU # in the Amazon store, and if so link the products.
5. From the Feed Submissions dashboard, you can see the status of your submission. It will change from SUBMITTED to IN_PROGRESS to DONE. When it's done you can view the report results and the raw XML that was sent back from Amazon.

I'm not sure what "Switch to Amazon Fulfillment" does. Does it make ALL the products in the Oscar store fulfilled by Amazon, or just some of them? And if just some of them, how do you indicate which ones?

[roadsideseb]

I've started writing up some documentation in the Getting Started section. I've got your first two points covered and will write up some more details tomorrow.

[natea]

Great to see the getting started guide starting to fill out! Keep 'em coming! :)