[docs] AWS S3 config details added (#1300)

* AWS S3 config details added

It was interesting to note that since presigned urls are used buckets dont need to be exposed publically. this was an interesting change compared to other mastodon specific s3 bucket guides hence documented here for correct directions.

* Update storage.md

1. Added AWS identified to make it clear its aws specific.
2. Adjusted text around data migration

* updation as requested

Refining the doc as per request.

docs/configuration/storage.md

@@ -62,6 +62,62 @@ storage-s3-secret-key: ""
 storage-s3-bucket: ""
 ```
 
+### AWS S3 Bucket Configuration
+
+#### Bucket Created
+GoToSocial by default creates signed URL's which means we dont need to change anything major on the policies of the bucket.
+Here are the steps to follow for bucket creation
+
+1. Login to AWS -> select S3 as service.
+2. click Create Bucket
+3. Provide a unique name and avoid adding "." in the name
+4. Do not change the public access settings (Let them be on "block public access" mode)
+
+#### AWS ACCESS KEY Configuration
+
+1. In AWS Console -> IAM (under Security, Identity, & Compliance)
+2. Add a user with programatic api's access
+3. We recommend setting up below listed policy, replace <bucketname> with your buckets name
+
+```json
+{
+    "Statement": [
+        {
+            "Effect": "Allow",
+            "Action": "s3:ListAllMyBuckets",
+            "Resource": "arn:aws:s3:::*"
+        },
+        {
+            "Effect": "Allow",
+            "Action": "s3:*",
+            "Resource": [
+                "arn:aws:s3:::<bucket_name>",
+                "arn:aws:s3:::<bucket_name>/*"
+            ]
+        }
+    ]
+}
+```
+
+4. Provide the values in config above
+  
+  * storage-s3-endpoint -> should be your bucket location say `s3.ap-southeast-1.amazonaws.com`
+  * storage-s3-access-key -> Access key you obtained for the user created above
+  * storage-s3-secret-key -> Secret key you obtained for the user created above
+  * storage-s3-bucket -> Keep this as the <bucketname> that you created just now.
+
+
+
+#### Migrating data from local storage to AWS s3 bucket
+
+This step is only needed if you have a running instance. Ignore this if you are setting up a fresh instance. 
+We have provided [s3cmd](https://github.com/s3tools/s3cmd) command for the copy operation.
+
+```bash
+s3cmd sync --add-header="Cache-Control:public, max-age=315576000, immutable" ./ s3://<bucket name>
+```
+
+
 ### Migrating between backends
 
 Currently, migration between backends is freely possible. To do so, you only