Added reminder to not enable APIGW cache during workshop for cost reasons

Author: kylesomers

README.md

@@ -54,6 +54,8 @@ Tokyo (ap-northeast-1) | [![Launch Zombie Workshop Stack into Tokyo with CloudFo
 
 **The baseline chat application is now configured and working! There is still important functionality missing and the Lambda Signal Corps needs you to build it out...so get started below!**
 
+*This workshop does not utilize API Gateway Cache. Please **KEEP THIS FEATURE TURNED OFF** as it is not covered under the AWS Free Tier and will incur additional charges.*
+
 ## Lab 1 - Typing Indicator
 
 **What you'll do in this lab...**