Update s3 configuration section to refer to s3_configuration.md

Author: beccyabraham

contributor_docs/installation.md

@@ -72,22 +72,9 @@ If you don't have the full server environment running, you can launch a one-off
 
 ## S3 Bucket Configuration
 
-Note that this is optional unless you are working on the part of the application that allows a user to upload images, videos, etc. Please refer to the following [gist](https://gist.github.com/catarak/70c9301f0fd1ac2d6b58de03f61997e3) to set up an S3 bucket to be used with this project.
+See [this configuration guide](./s3_configuration.md) for information about how to configure your own S3 bucket. These instructions were adapted from [this gist](https://gist.github.com/catarak/70c9301f0fd1ac2d6b58de03f61997e3).
 
-If your S3 bucket is in the US East (N Virginia) region (us-east-1), you'll
-need to set a custom URL base for it, because it does not follow the standard
-naming pattern as the rest of the regions. Instead, add the following to your
-environment/.env file, changing `BUCKET_NAME` to your bucket name. This is necessary because this override is currently treated as the full path to the bucket rather than as a proper base URL:
-`S3_BUCKET_URL_BASE=https://s3.amazonaws.com/{BUCKET_NAME}/`
-
-If you've configured your S3 bucket and DNS records to use a custom domain
-name, you can also set it using this variable. I.e.:
-
-`S3_BUCKET_URL_BASE=https://files.mydomain.com`
-
-For more information on using a custom domain, see this documentation link:
-
-http://docs.aws.amazon.com/AmazonS3/latest/dev/VirtualHosting.html#VirtualHostingCustomURLs
+Note that this is optional unless you are working on the part of the application that allows a user to upload images, videos, etc. 
 
 ## GitHub API Configuration