Add examples of different tagged release scenarios

Signed-off-by: Marcela Melara <[email protected]>

Author: marcelamelara

spec/README.md

@@ -27,13 +27,30 @@ together. See the [documentation] for more background and examples.
 ## Tagged Releases
 
 The latest [tagged release] version matches the [SemVer](https://semver.org)
-MAJ.MIN version of the Attestation Framework spec.
+MAJOR.MINOR version of the Attestation Framework spec.
 
 Backwards-compatible semantic updates to the spec (except predicates) are
-indicated through new tagged minor version releases.
-We use new tagged patch version releases to indicate updates to predicate
+indicated through new tagged MINOR version releases.
+We use new tagged PATCH version releases to indicate updates to predicate
 specifications and/or backwards-compatible changes to the language bindings.
 
+### Examples
+-   Attestation Framework tagged release v1.0.2 (PATCH version) incorporates
+    refinements to the predicate specification process, a new predicate type,
+    and a small patch to the Golang language bindings. None of these changes
+    affects the semantics of the core spec. The `_type` of a `Statement` is
+    still `https://in-toto.io/Statement/v1`.
+-   Tagged release v1.1.0 (MINOR version) generalizes the semantics of the
+    `DigestSet` field type to support any type of immutable identifier.
+    This change is backwards comptabile because cryptographic digests are
+    strongly recommended to achieve immutability, so any implementations that
+    only support cryptographic `DigestSet` still meet the modified semantics.
+    The `_type` of a `Statement` is still `https://in-toto.io/Statement/v1`
+    but a new entry in the `v1` CHANGELOG is added.
+-   Tagged release v2.0.0 (MAJOR version) changes the meaning of the
+    `predicateType` field. A new `v2` directory is added to `/spec` and the
+    `_type` of a `Statement` becomes `https://in-toto.io/Statement/v2`.
+
 ## Keywords
 
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",