added crypto examples to the docs

Author: duelingbenjos

README.md

@@ -122,6 +122,7 @@ def get_top_level_signer():
   - [Context](/docs/concepts/context.md)
   - [Functions](/docs/concepts/functions.md)
   - [Hashing](/docs/concepts/hashing.md)
+  - [Crypto](/docs/concepts/crypto.md)
   - [Imports](/docs/concepts/imports.md)
   - [Model](/docs/concepts/model.md)
   - [Randoms](/docs/concepts/randoms.md)

docs/concepts/crypto.md

@@ -0,0 +1,15 @@
+## Crypto Standard Library
+
+In this example, the verify_signature function is an exported function in a Xian smart contract. It takes a verification key (vk), a message (msg), and a signature (signature). It uses the verify function from the crypto module to check if the signature is valid for the given message and verification key. The result (True or False) is then returned. This can be used to ensure data integrity and authenticity in transactions within the smart contract environment.
+
+This module uses the `PyNaCl` library under the hood, employing the `Ed25519` signature scheme.
+
+```python
+@export
+def verify_signature(vk: str, msg: str, signature: str):
+    # Use the verify function to check if the signature is valid for the given message and verification key
+    is_valid = crypto.verify(vk, msg, signature)
+    
+    # Return the result of the verification
+    return is_valid
+```