feat: init commit, fork from libsm

docs/sm3.md

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+# SM3
+
+SM3 is a hash function. To use SM3 in libsm:
+
+1. Make sure that your data is `&[u8]`.
+
+2. Create a `SM3Hash`. 
+
+3. Get the digest.
+
+Sample:
+
+```rust
+use libsm::sm3::Sm3Hash;
+
+let string = String::from("sample");
+let mut hash = Sm3Hash::new(string.as_bytes());
+let digest: [u8;32] = hash.get_hash();
+```
+