feat: add Heroku proc file for starting the web server

Also support for changing port where the server is running

Procfile

@@ -0,0 +1 @@
+web: ./target/release/rustybeer-server

README.md

@@ -35,7 +35,8 @@ To start the server:
 cargo run --bin rustybeer-server
 ```
 
-You can access the OpenAPI UI from http://localhost:3000/docs
+You can access the OpenAPI UI from http://localhost:3000/docs. To change the
+port number, you can define environment variable PORT.
 
 ## Testing
 

rustybeer-server/src/main.rs

@@ -1,6 +1,7 @@
 mod handlers;
 
 use rweb::*;
+use std::env;
 
 /// Renders the homepage. TODO: Change this to return HTML
 /// and link to /docs
@@ -9,13 +10,20 @@ fn default() -> String {
     return "Check the /docs".to_string();
 }
 
+fn get_port() -> u16 {
+    match env::var("PORT") {
+        Ok(val) => val.parse::<u16>().unwrap(),
+        _ => 3000,
+    }
+}
+
 #[tokio::main]
 async fn main() {
     let (spec, filter) = openapi::spec().build(move || {
         handlers::abv::abv().or(handlers::abv::fg().or(handlers::beer_style::search()))
     });
 
     serve(filter.or(default()).or(openapi_docs(spec)))
-        .run(([0, 0, 0, 0], 3000))
+        .run(([0, 0, 0, 0], get_port()))
         .await;
 }