Merge pull request #13352 from thaJeztah/add_missing_codehints

Add missing code-hints, and minor markdown edits

docs/garbage-collection.md

@@ -100,7 +100,7 @@ gives a clear indication of items eligible for deletion.
 
 The config.yml file should be in the following format:
 
-```
+```yaml
 version: 0.1
 storage:
   filesystem:

docs/notifications.md

@@ -159,7 +159,7 @@ request coming to an endpoint.
 
 An example of a full event may look as follows:
 
-```
+```http request
 GET /callback HTTP/1.1
 Host: application/vnd.docker.distribution.events.v1+json
 Authorization: Bearer <your token, if needed>

docs/storage-drivers/s3.md

@@ -84,6 +84,7 @@ The following AWS policy is required by the registry for push and pull. Make sur
   ]
 }
 ```
+
 See [the S3 policy documentation](http://docs.aws.amazon.com/AmazonS3/latest/dev/mpuAndPermissions.html) for more details.
 
 # CloudFront as Middleware with S3 backend
@@ -135,7 +136,7 @@ are still directly written to S3.
 
 The following example shows a minimum configuration:
 
-```
+```yaml
 ...
 storage:
   s3: