docs: update cyclone-dx documentation (#2983)

* chore: update docs to show 1.6 for cyclone-dx by default
* chore: update README showing version information for formats

---------

Signed-off-by: Christopher Phillips <[email protected]>

README.md

@@ -105,8 +105,10 @@ syft <image> -o <format>
 Where the `formats` available are:
 - `syft-json`: Use this to get as much information out of Syft as possible!
 - `syft-text`: A row-oriented, human-and-machine-friendly output.
-- `cyclonedx-xml`: A XML report conforming to the [CycloneDX 1.4 specification](https://cyclonedx.org/specification/overview/).
-- `cyclonedx-json`: A JSON report conforming to the [CycloneDX 1.4 specification](https://cyclonedx.org/specification/overview/).
+- `cyclonedx-xml`: A XML report conforming to the [CycloneDX 1.6 specification](https://cyclonedx.org/specification/overview/).
+- `[email protected]`: A XML report conforming to the [CycloneDX 1.5 specification](https://cyclonedx.org/specification/overview/).
+- `cyclonedx-json`: A JSON report conforming to the [CycloneDX 1.6 specification](https://cyclonedx.org/specification/overview/).
+- `[email protected]`: A JSON report conforming to the [CycloneDX 1.5 specification](https://cyclonedx.org/specification/overview/).
 - `spdx-tag-value`: A tag-value formatted report conforming to the [SPDX 2.3 specification](https://spdx.github.io/spdx-spec/v2.3/).
 - `[email protected]`: A tag-value formatted report conforming to the [SPDX 2.2 specification](https://spdx.github.io/spdx-spec/v2.2.2/).
 - `spdx-json`: A JSON report conforming to the [SPDX 2.3 JSON Schema](https://github.com/spdx/spdx-spec/blob/v2.3/schemas/spdx-schema.json).
@@ -115,6 +117,8 @@ Where the `formats` available are:
 - `syft-table`: A columnar summary (default).
 - `template`: Lets the user specify the output format. See ["Using templates"](#using-templates) below.
 
+Note that flags using the @<version> can be used for earlier versions of each specification as well.
+
 ### Supported Ecosystems
 
 - Alpine (apk)