docs(config): add example

Author: CSUwangj

.gitignore

@@ -12,6 +12,7 @@
 /target
 
 .env
-config.ron
+*.ron
+!example.ron
 test/*
 .vscode

example.ron

@@ -0,0 +1,41 @@
+Configuration(
+  practice: (
+    lab_categories: [
+      (
+        id: "classical",
+        name: [
+          (
+            language: "en-US",
+            text: "Classical"
+          ),
+          (
+            language: "zh-CN",
+            text: "古典密码学"
+          )
+        ],
+        labs: [
+          (
+            id: "affine",
+            resources: [
+              (
+                language: "zh-CN",
+                name: "仿射加密",
+                resource: "practice/classical/affine/zh.md"
+              )
+            ],
+            endpoints: [
+              (
+                host: "localhost",
+                port: 10020
+              ),
+              (
+                host: "192.168.16.128",
+                port: 10020
+              ),
+            ]
+          )
+        ]
+      )
+    ]
+  )
+)         

src/opts.rs

@@ -13,7 +13,7 @@ pub struct Opt {
     pub log_level: u32,
 
     /// configuration file's, check example for more details
-    #[structopt(default_value = "config.toml", env = "CONFIG", parse(from_os_str))]
+    #[structopt(default_value = "config.ron", env = "CONFIG", parse(from_os_str))]
     pub config: PathBuf,
 
     /// static file path to be serve