docs: Add CHANGELOG for v0.1 release

CHANGELOG.md

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+## 2022-09-19 v0.1
+
+Initial beta release.
+
+This release contain:
+
+- RLN Module with API to manage, compute and verify [RLN](https://rfc.vac.dev/spec/32/) zkSNARK proofs and RLN primitives.
+- This can be consumed either as a Rust API or as a C FFI. The latter means it can be easily consumed through other environments, such as [Go](https://github.com/status-im/go-zerokit-rln/blob/master/rln/librln.h) or [Nim](https://github.com/status-im/nwaku/blob/4745c7872c69b5fd5c6ddab36df9c5c3d55f57c3/waku/v2/protocol/waku_rln_relay/waku_rln_relay_types.nim).
+
+It also contains the following examples and experiments:
+
+- Basic [example wrapper](https://github.com/vacp2p/zerokit/tree/master/multiplier) around a simple Circom circuit to show Circom integration through ark-circom and FFI.
+- Experimental [Semaphore wrapper](https://github.com/vacp2p/zerokit/tree/master/semaphore).
+
+Feedback welcome! You can either [open an issue](https://github.com/vacp2p/zerokit/issues) or come talk to us in our [Vac Discord](https://discord.gg/PQFdubGt6d) #zerokit channel.