feat(example): added an example of packaging a rust app from github (#124)

* better caching when building docker images for app

Reviewed-on: NationTech/harmony#124
Reviewed-by: johnride <jg@nationtech.io>
Co-authored-by: Willem <wrolleman@nationtech.io>
Co-committed-by: Willem <wrolleman@nationtech.io>

examples/rust/src/main.rs

@@ -20,8 +20,9 @@ async fn main() {
     let application = Arc::new(RustWebapp {
         name: "harmony-example-rust-webapp".to_string(),
         domain: Url::Url(url::Url::parse("https://rustapp.harmony.example.com").unwrap()),
-        project_root: PathBuf::from("./webapp"), // Relative from 'harmony-path' param
+        project_root: PathBuf::from("./webapp"),
         framework: Some(RustWebFramework::Leptos),
+        service_port: 3000,
     });
 
     let discord_receiver = DiscordWebhook {