wip explaining config crate

blueprint/config/README.md.liquid

@@ -14,10 +14,20 @@ pub struct Config {
 }
 ```
 
+TODO
+- mention that database config is supposed to be changed by environment variables only i.e. `APP_DATABASE__URL`, `APP_DATABASE__NAME`.
+  - Add rationale i.e. avoid accidentally pushing database connection url to the repo.
+- explain, possibly rename `app.toml` to `global.toml` alternatively it should say `server.toml` to match the `ServerConfig` struct name,
+indicating its content changes only that particular struct.
+- Add flow diagram that describes how config is built from different sources: app.toml -> environments/[env].toml -> APP_SERVER__NESTED_FIELD environment variables.
+- Changing app.toml and environment files only changes the top level config and not inside Server. How to add and change Server config using config files?
+
 Gerust uses [figment](https://crates.io/crates/figment) to populate the `Config` struct from environment variables and TOML files such that:
 
 * the `ServerConfig` that contains interface and port to bind to, is populated from the `APP_SERVER__IP` and `APP_SERVER__PORT` environment variables.
 {%- unless template_type == "minimal" %}
 * the `DatabaseConfig` that contains the connection URL for the database is populated from the `APP_DATABASE__URL` environment variable.
 {%- endunless %}
 * any application-specific configuration values are read from the `app.toml` and environment-specific configuration files such that settings in the environment-specific configuration files override values for the same setting in `app.toml`.
+
+

blueprint/config/environments/production.toml

@@ -1 +1,3 @@
 # add config settings for the production environment here…
+[server]
+match_lifespan = 300

blueprint/config/src/lib.rs.liquid

@@ -134,12 +134,12 @@ where
     };
 
     let config: T = Figment::new()
+        .merge(Serialized::defaults(ServerConfig::default()).key("server"))
         .merge(Toml::file("config/app.toml"))
         .merge(Toml::file(format!(
             "config/environments/{}",
             env_config_file
         )))
-        .merge(Serialized::defaults(ServerConfig::default()).key("server"))
         .merge(Env::prefixed("APP_").split("__"))
         .extract()
         .context("Could not read configuration!")?;