Added serde as an optional dependency

Cargo.lock

@@ -50,6 +50,7 @@ dependencies = [
  "android-tzdata",
  "iana-time-zone",
  "num-traits",
+ "serde",
  "windows-targets",
 ]
 
@@ -141,6 +142,27 @@ name = "r701"
 version = "0.1.0"
 dependencies = [
  "chrono",
+ "serde",
+]
+
+[[package]]
+name = "serde"
+version = "1.0.200"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddc6f9cc94d67c0e21aaf7eda3a010fd3af78ebf6e096aa6e2e13c79749cce4f"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.200"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "856f046b9400cee3c8c94ed572ecdb752444c24528c035cd35882aad6f492bcb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
 ]
 
 [[package]]