Add serde feature and dependency

CHANGELOG.md

@@ -13,6 +13,9 @@ Procedure when bumping the version number:
 
 ## Unreleased
 
+### Added
+- `serde` feature
+
 ### Changed
 - **(breaking)**
   Error handling of `Action`s is now more complex but more powerful. In

Cargo.toml

@@ -4,8 +4,10 @@ version = "0.1.0"
 edition = "2021"
 
 [features]
+serde = ["dep:serde"]
 tokio = ["dep:tokio"]
 
 [dependencies]
 rusqlite = "0.28"
+serde = { version = "1.0", optional = true }
 tokio = { version = "1.25", features = ["sync"], optional = true }