docs: update readme

Author: kwaa

README.md

@@ -1,9 +1,26 @@
 # Moeru AI Blog
 
-## Local Development
+## Development
 
 ```bash
 deno task build # build
 deno task serve # serve
 deno task cms # cms
 ```
+
+## Writing new post
+
+Only Moeru AI members can add new posts. (nonetheless, all typo fix are welcome)
+
+Add a new `.md` file to `src/posts` based on the following format:
+
+```ts
+interface Data {
+  title: string
+  date: string // 'YYYY-MM-DD'
+  author: string // multiple authors example: 'Foo, Bar'
+  tags?: string[]
+}
+```
+
+Have fun!