Add LICENSE file

Author: kseo

Cargo.toml

@@ -3,7 +3,7 @@ name = "codechain-db"
 version = "0.2.0"
 authors = ["CodeChain Team <[email protected]>", "Parity Technologies <[email protected]>"]
 description = "Databases that CodeChain uses"
-license = "GPL-3.0"
+license = "AGPL-3.0"
 edition = "2018"
 
 [dependencies]