docs(fsharp): add formatter docs

modules/lang/fsharp/README.org

@@ -48,6 +48,13 @@ pacman -S mono
 ** LSP
 The language server is automatically installed by [[https://github.com/emacs-lsp/lsp-mode/blob/master/clients/lsp-fsharp.el][lsp-fsharp]].
 
+** Fantomas
+Fantomas is used for formatting via [[doom-module::editor format]] and can be installed as a [[https://dotnet.microsoft.com/en-us/download][dotnet]] tool. 
+
+#+begin_src shell
+dotnet tool install -g fantomas-tool
+#+end_src
+
 * TODO Usage
 #+begin_quote
  🔨 This module has no usage documentation yet. [[doom-contrib-module:][Write some?]]