Add readme

zetaclient/tss/readme.md

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+# Zetaclient TSS Overview
+
+(Threshold Signature Scheme)
+
+This package wraps the go-tss library, providing a high-level API for signing arbitrary digests using TSS.
+The underlying go-tss library relies on tss-lib.
+
+## What is a Digest?
+
+A digest is simply a byte slice (`[]byte`), typically representing a transaction hash or other cryptographic input.
+The API allows secure signing of these digests in a distributed manner.
+
+## Architecture Overview
+
+This is the approximate structure of the TSS implementation within Zetaclient:
+
+```text
+zetaclientd(
+    tss.Service(
+        gotss.Server(libp2p()) 
+    )
+)
+```
+
+## Package Structure
+
+- `setup.go`: Initializes the go-tss TSS server and the **Service** wrapper of this package.
+- `keygen.go`: Manages the key generation ceremony, creating keys used by TSS.
+- `service.go`: Implements the **Service** struct, offering methods for signing and verifying digests.
+- Other Files: Utilities and supporting tools for TSS operations.
+
+## Links
+
+- `go-tss`: https://github.com/zeta-chain/go-tss
+- `tss-lib`: https://github.com/zeta-chain/tss-lib