Update documentation for module-indent option

Author: HPRIOR

CHANGES.md

@@ -6,6 +6,19 @@ profile. This started with version 0.26.0.
 
 ## unreleased
 
+### Added 
+
+- Added option `module-indent` option (#2711, @HPRIOR) to control the indentation
+  of items within modules. This affects modules and signatures. For example, 
+  module-indent=4:
+  ```ocaml
+  module type M = sig
+      type t
+
+      val f : (string * int) list -> int
+  end
+  ```
+
 ### Deprecated
 
 - Starting in this release, ocamlformat can use cmdliner >= 2.0.0. When that is

doc/manpage_ocamlformat.mld

@@ -295,6 +295,10 @@ OPTIONS (CODE FORMATTING STYLE)
            the offset of the previous line. The default value is 68. Cannot
            be set in attributes.
 
+       --module-indent=COLS
+           Indentation of items within modules (COLS columns). The default
+           value is 2.
+
        --module-item-spacing={compact|sparse|preserve}
            Spacing between items of structures and signatures. compact will
            not leave open lines between one-liners of similar sorts. sparse