Minor changes to readme

Dependencies

• [2] B6XN375L Improve README
• [3] KAYDCVNP Add README

Change contents

• replacement in README.md at line 12
  [2.321]→[2.321:381](∅→∅)
  − * `#` is `flip ($)`, `<#>` is `flip <$>`, `Unit` is `()`.
  [2.321]

  [2.381]
  + * `#` is `flip ($)`

  + * `<#>` is `flip <$>`

  + * `Unit` is `()`