doc: update README.md

README.md

@@ -1,2 +1,56 @@
 # hakurei
 
+## Namuwiki Parser
+
+Dump download: https://mu-star.net/wikidb
+
+### Extract Category
+
+Most articles have categories.
+
+```rs
+fn main() {
+  let js = load_dump();
+  extract_category(js);
+}
+```
+
+#### (Example) Find By Category
+
+If you want to fetch `Article` rather than `Title`, modify the code appropriately.
+
+```rs
+fn find_by_category<'a>(js: &'a Vec<Article>, what: &str) -> Vec<&'a str> {
+    let mut result: Vec<&str> = Vec::new();
+
+    for x in js {
+        let category = x.categories();
+
+        if category.iter().any(|x| x.starts_with(what)) {
+            result.push(&x.title);
+        }
+    }
+
+    result.sort_by(|a, b| a.cmp(b));
+
+    result
+}
+```
+
+### Title indexing
+
+Before using, you must create title index file.
+
+```rs
+fn main() {
+  create_title_index();
+}
+```
+
+```rs
+fn main() {
+  let mut index = TitleIndex::load();
+
+  println!("{}", index.get("하쿠레이 신사").unwrap().text);
+}
+```