Add minimal S3 configuration for Corso (#158)

docs/docs/concepts/corso-repository-and-configuration.md

@@ -4,9 +4,38 @@ sidebar_position: 1
 
 # Repositories and configuration
 
-How to configure Corso:
+## Object storage configuration
+
+Corso stores all backup data in an object storage system. Corso supports Amazon Web
+Services (AWS) S3, Google Cloud Storage (GCS), Azure Blob, and S3-compatible systems.
 
 ```mermaid
 graph TD;
-    Corso-->S3;
+    Corso-->ObjectStorage;
+```
+
+### Amazon S3 and S3-compatible systems
+
+Corso needs the following permissions for AWS S3 and S3-compatible object storage systems:
+
+```json
+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Effect": "Allow",
+            "Action": [
+                "s3:PutObject",
+                "s3:GetObject",
+                "s3:ListBucket",
+                "s3:DeleteObject",
+                "s3:GetBucketLocation",
+            ],
+            "Resource": [
+                "arn:aws:s3:::${BUCKET_NAME}",
+                "arn:aws:s3:::${BUCKET_NAME}/*"
+            ]
+        }
+    ]
+}
 ```