Draft module doc

@@tetsuyamorishita please fill the module documentation with some text. Thanks!

user-doc/LOGMFD.md

+\page LOGMFD xxxxxxxx
+
+<!-- 
+description: xxxxxxxxx
+authors: xxxxxxxxx
+reference: xxxxxxxxxx
+-->
+
+## Overview
+
+xxxxxxxxx
+
+## Installation 
+This module is not installed by default. Add '\-\-enable-modules=logmfd' to your './configure' command when building PLUMED to enable these features.
+
+## Usage
+Currently, all features of the LOGMFD module are included in a single LOGMFD bias function: \ref LOGMFD
+
+## Module Contents
+- \subpage LOGMFDMODBias
+
+\page LOGMFDMODBias Biases Documentation
+
+The following list contains descriptions of biases developed for the PLUMED-LOGMFD module. They can be used in combination with other biases outside of the LOGMFD module.
+
+@LOGMFDMOD_BIAS@