Update chess game README to include DynamoDB AutoScaling

At the end of June I created a free tier account and followed the chess game tutorial. Today I got charged for the use of excess alarms. I was unaware that in following this tutorial 40 alarms were created, with only 10 allowed within the free tier.

When creating the DynamoDB tables the instructions are outdated. They say to accept the default capacity settings, and to "select or clear **Use Basic Alarms**. We will not cover them in this tutorial."

Based on these instructions I deleted the alarms listed in the table, but (since mid June) the default capacity settings include auto scaling which (without notification) adds 8 alarms per table.

The instructions should either include a warning about the additional alarms, or suggest turning off auto scaling before the table is created, and then delete the table alarms.