fix: markdown style for the About page

src/content/spec/about.md

@@ -1,2 +1,7 @@
-## About
-This is the about page.
+# About
+This is the demo site for [Fuwari](https://github.com/saicaca/fuwari).
+
+> ### Sources of images used in this site
+> - [Unsplash](https://unsplash.com/)
+> - [星と少女](https://www.pixiv.net/artworks/108916539) by [Stella](https://www.pixiv.net/users/93273965)
+> - [Rabbit - v1.4 Showcase](https://civitai.com/posts/586908) by [Rabbit_YourMajesty](https://civitai.com/user/Rabbit_YourMajesty)