docs: align media types in table (CycloneDX#561)

to mimic style from website
https://cyclonedx.org/specification/overview/

---------

Signed-off-by: Jan Kowalleck <jan.kowalleck@owasp.org>

Author: jkowalleck

README.md

@@ -47,15 +47,13 @@ free, open source, and proprietary tools and solutions that support the CycloneD
 The following media types are officially registered with IANA:
 
 | Media Type | Format | Assignment |
-| ------- | --------- | --------- |
-| application/vnd.cyclonedx+xml | XML | [IANA](https://www.iana.org/assignments/media-types/application/vnd.cyclonedx+xml) |
-| application/vnd.cyclonedx+json | JSON | [IANA](https://www.iana.org/assignments/media-types/application/vnd.cyclonedx+json) |
+|------------|--------|------------|
+| `application/vnd.cyclonedx+xml` | XML | [IANA](https://www.iana.org/assignments/media-types/application/vnd.cyclonedx+xml) |
+| `application/vnd.cyclonedx+json` | JSON | [IANA](https://www.iana.org/assignments/media-types/application/vnd.cyclonedx+json) |
+| `application/x.vnd.cyclonedx+protobuf` | Protocol Buffer | |
 
 Specific versions of CycloneDX can be specified by using the version parameter. For example: `application/vnd.cyclonedx+xml; version=1.6`.
 
-The officially supported media type for Protocol Buffer format is `application/x.vnd.cyclonedx+protobuf`.
-
-
 ## Release History
 
 | Version           | Release Date    |