[Docs] Document the OCaml support

docs/index.md

@@ -92,7 +92,7 @@ The following programming languages have enhanced support in Prelude:
 - [Lisp Base](modules/lisp.md) (common foundation for Lisp modules)
 - Lua
 - Markdown
-- OCaml
+- [OCaml](modules/ocaml.md)
 - Org Mode
 - Perl
 - [Python](modules/python.md)

docs/modules/ocaml.md

@@ -0,0 +1,49 @@
+# Prelude OCaml
+
+!!! Note
+
+    This module builds on top of the shared [Programming](programming.md) module.
+
+## Overview
+
+Prelude provides powerful out-of-the-box experience for programming in OCaml:
+
+- major-mode for editing OCaml code (`tuareg-mode`)
+- integration with `utop`, OCaml's modern top-level (you can think of it as a REPL)
+- linting via `flycheck` or `merlin`
+- code completion via `merlin`
+
+You can get similar experience using OCaml's LSP server, but it's based on Merlin internally and the setup with LSP is a bit more involved.
+
+## Packages
+
+When the `prelude-ocaml` is enabled it will install 3 packages:
+
+- `tuareg-mode`
+- `utop`
+- `merlin`
+
+## Environment Setup
+
+These setups for ocaml assume that you are using the OPAM package
+manager (http://opam.ocaml.org/).
+
+Because of the apparent complexity of getting Emacs environment
+variables setup to use opam correctly, it is instead easier to use
+opam itself to execute any necessary commands.
+
+Also, the standard OCaml toplevel usage has been replaced in favor
+of UTOP, the universal toplevel, and we assume that you are using
+the Jane Street Core libraries rather than the regular OCaml
+standard libraries
+
+The minimum required setup for using Prelude's OCaml setup would be
+to install OPAM, and then, minimally `opam install core utop'.  A
+good getting started guide is available at
+https://dev.realworldocaml.org/install.html
+
+## Configuration
+
+Prelude disables Merlin's own linting in favor of Flycheck. It also
+leverages Merlin's company-mode backend instead of using directly
+Merlin's rudimentary auto-completion system.