docs: Add docs for s3 blobs (#1477)

## This PR
Intent of this PR is to add the docs that were missing from #1449 

### Notes
Happy holidays yall.

---------

Signed-off-by: Dave Josephsen <[email protected]>
Co-authored-by: Michael Beemer <[email protected]>
Co-authored-by: Todd Baert <[email protected]>

Author: 3 people

docs/concepts/syncs.md

@@ -97,10 +97,24 @@ flagd start --uri azblob://my-container/my-flags.json
 
 In this example, assuming the environment variable AZURE_STORAGE_ACCOUNT is set to `myaccount`, and other options are not set, the service URL will be:
 `https://myaccount.blob.core.windows.net/my-container/my-flags.json`.
-This is expected be a valid service URL accessible by flagd (either by being public or together with environment variable credentials).
+This is expected to be a valid service URL accessible by flagd (either by being public or together with environment variable credentials).
 The polling interval can be configured.
 See [sync source](../reference/sync-configuration.md#source-configuration) configuration for details.
 
+### S3 sync
+
+The S3 sync provider fetches flags from an S3 bucket and periodically polls for flag definition updates.
+It uses [AWS standardized credentials chain](https://docs.aws.amazon.com/sdkref/latest/guide/standardized-credentials.html) to authorize the calls to AWS.
+
+```shell
+flagd start --uri s3://my-bucket/my-flags.json
+```
+
+In this example, `s3://my-bucket/my-flags.json` is expected to be a valid URI accessible by flagd
+(either by being public or together with the appropriate credentials read from a file or via the environment as described in the AWS docs linked above).
+The polling interval is configurable.
+See [sync source](../reference/sync-configuration.md#source-configuration) for details.
+
 ## Merging
 
 Flagd can be configured to read from multiple sources at once, when this is the case flagd will merge all flag definition into a single

docs/reference/sync-configuration.md

@@ -20,6 +20,7 @@ it is passed to the correct implementation:
 |  [grpc](#custom-grpc-target-uri) | `[ envoy \| dns \| uds\| xds ]://` | `envoy://localhost:9211/test.service` |
 | `gcs`                 | `gs://`                | `gs://my-bucket/my-flags.json`        |
 | `azblob`              | `azblob://`            | `azblob://my-container/my-flags.json` |
+| `s3`              | `s3://`            | `s3://my-bucket/my-flags.json` |
 
 ### Custom gRPC Target URI