Adding readme to repo

Author: davesc63

README.md

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+**AWS CloudFront Cache Invalidation**
+
+This is a small function that can be invoked to invalidate the cache of a CloudFront Distribution.
+
+Updated slightly from the aws-cloudfront-cache-invalidation script to send a response to CodePipeline on success.
+
+The purpose of this function is to be called as required as a standalone function when you need your cache invalidated and the functionality is not in-built to the tool or service you are using.
+**Example**: This function is called during the Deploy stage of a CodePipeline to invalidate the cache of a CloudFront Distribution for a static website hosted in Amazon S3
+
+**How to use**
+1. Create a new **Lambda** function
+2. Select **Python 3.8** as the runtime
+3. Copy the source code into your function
+4. Create execution role and assign permissions to your cloudfront distribution
+5. Create an **Environment Variable** with a _key_ of DISTRIBUTION_ID and a _value_ of your CloudFront Distribution
+6. Deploy function
+
+
+**Note**
+This function invalidates the entire cache. To select paths update the **items* sections within the function