docs: add missing backticks in documentation

this improve readability of documentation.
enable associated clippy lint `doc_markdown`

src/rpc/layout/helper.rs

@@ -162,7 +162,7 @@ impl LayoutHelper {
 	}
 
 	/// Returns the latest layout version for which it is safe to read data from,
-	/// i.e. the version whose version number is sync_map_min
+	/// i.e. the version whose version number is `sync_map_min`
 	pub fn read_version(&self) -> Result<&LayoutVersion, Error> {
 		let sync_min = self.sync_map_min;
 		let versions = self.versions()?;