Add incomplete list of changes

Changes-v3.md

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+# Incompatible Changes from v2 to v3
+
+These are changes that are incompatible with the v2.x.x version.
+
+* [Detailed List of Changes](#detailed-list-of-changes) - A comprehensive list of changes from v2 to v3
+
+# Detailed list of changes
+
+## Module
+
+* This module now requires Go 1.20.x
+
+* All `xxx.Get()` methods have been changed from `Get(string) (interface{}, error)` to
+  `Get(string, interface{}) error`, where the second argument should be a pointer
+  to the storage destination of the field.
+
+## JWS
+
+* Iterators have been completely removed.
+* As a side effect of removing iterators, some methods such as `Copy()` lost the
+  `context.Context` argument
+
+## JWE
+
+* Iterators have been completely removed.
+* As a side effect of removing iterators, some methods such as `Copy()` lost the
+  `context.Context` argument
+
+## JWK
+
+* Iterators have been completely removed.
+
+* `jwk/x25519` has been removed. To use X25519 keys, use `(crypto/ecdh).PrivateKey` and
+  `(crypto/ecdh).PublicKey`. Similarly, internals have been reworked to use `crypto/ecdh`
+
+* Parsing has completely been reworked. It is now possible to add your own `jwk.KeyParser`
+  to generate a custom `jwk.Key` that this library may not natively support. Also see
+  `jwk.RegisterKeyParser()`
+
+* `jwk.KeyProbe` has been added to aid probing the JSON message. This is used to
+  guess the type of key described in the JSON message before deciding which concrete
+  type to instantiate, and aids implementing your own `jwk.KeyParser`. Also see
+  `jwk.RegisterKeyProbe()`
+
+* Conversion between raw keys and `jwk.Key` can be customized using `jwk.KeyConverter`.
+  Also see `jwk.RegisterKeyConverter()`
+
+* Added `jwk/ecdsa` to keep track of which curves are available for ECDSA keys.