document version match process

Author: bart0sh

SPEC.md

@@ -33,6 +33,8 @@ Released versions of the spec are available as Git tags.
 |        |   | Add `AdditionalGIDs` to `ContainerEdits` |
 | v0.8.0 |   | Remove .ToOCI() functions from specs-go package. |
 
+*Note*: spec loading fails on unknown fields and when minimal required version is higher than the version specified in the spec. Minimum required version is determined based on the usage of fields mentioned in the table above. For example minimal required version is v0.6.0 if `Annotations` field is used in the spec, but `IntelRdt` is not. Golang null default values are used for all new fields so the spec remains valid when loading older spec versions.
+
 *Note*: The initial release of a **spec** with version `v0.x.0` will be tagged as
 `v0.x.0` with subsequent changes to the API applicable to this version tagged as `v0.x.y`.
 ## Overview