Adds missing documents to components/index file.

Author: Fabrício Zimmerer Murta

components/readme.md

@@ -12,12 +12,13 @@ Retype flavored Markdown supports custom components, including:
 - [Code block](code-block.md)
 - [Code snippet](code-snippet.md)
 - [Column](column.md)
+- [Embed](embed.md)
 - [Emoji](emoji.md)
 - [File download](file-download.md)
 - [Icon](icon.md)
 - [Image](image.md)
 - [List](list.md)
-- [Math formula](math-formula.md)
+- [Math formulas](math-formulas.md)
 - [Mermaid](mermaid.md)
 - [Panel](panel.md)
 - [Reference link](reference-link.md)