Vendor dependencies for 0.3.0 release

vendor/sysinfo/md_doc/serde.md

@@ -0,0 +1,12 @@
+
+With the `serde` feature enabled, you can then serialize `sysinfo` types. Let's see an example with `serde_json`:
+
+```
+use sysinfo::System;
+
+let mut sys = System::new_all();
+// First we update all information of our `System` struct.
+sys.refresh_all();
+
+println!("{}", serde_json::to_string(&sys).unwrap());
+```