document buildType config for slsa/v2alpha2 format. This is

documentation for tektoncd#895

docs/config.md

@@ -112,7 +112,14 @@ You can read more about Grafeas notes and occurrences [here](https://github.com/
 | Key | Description | Supported Values | Default |
 | :--- | :--- | :--- | :--- |
 | `builder.id` | The builder ID to set for in-toto attestations | | `https://tekton.dev/chains/v2`|
-
+| `builddefinition.buildtype` | The buildType for in-toto attestations | `https://tekton.dev/chains/v2/slsa`, `https://tekton.dev/chains/v2/slsa-tekton` | `https://tekton.dev/chains/v2/slsa`|
+
+> NOTE:
+> Considerations for the builddefinition.buildtype parameter:
+> * It is only valid for slsa/v2alpha2 configurations (see TaskRun or PipelineRun configuration). 
+> * The parameter can take one of two values:
+>   * https://tekton.dev/chains/v2/slsa: This buildType strictly conforms to the slsav1.0 spec.
+>   * https://tekton.dev/chains/v2/slsa-tekton: This buildType also conforms to the slsav1.0 spec, but adds additional informaton specific to Tekton. This information includes the PipelinRun/TaskRun labels and annotations as internalParameters. It also includes capturing each pipeline task in a PipelinRun under resolvedDependencies.
 ### Sigstore Features Configuration
 
 #### Transparency Log