Document members directory module.

MODULES.md

@@ -351,6 +351,34 @@ the result using 3rd passes and finalizes the result in the 4th pass.
 
 ### Members Directory
 
+This module encapsulates the members base directory format as
+documented in ```MEMBERS.md``` document.
+
+Each member file should have a 4-digit name identical to member id and
+optional symlinks with human-known names of the members. The module
+can correctly handle a situation where the 4-digit id is a symlink to
+arbitrarily named file.
+
+In first pass it extracts all files and symlinks to them, binds them
+together and makes sure the 4-digit name is used as id and the regular
+file is read when loading its contents.
+
+    (load-members-dir dn)
+
+* ```dn``` - directory name (path)
+
+Scans given directory and returns a dictionary of canonical names as
+keys and lists of alias symlinks as values.
+
+    (members-dir-load-member mdir fname symlinks)
+
+* ```mdir``` - members directory name (path)
+* ```fname``` - file name inside ```mdir``` (without path)
+* ```symlinks``` - a list of symlinks to ```fname```
+
+Creates an initial member record and uses ```load-member-file``` to
+load, parse and interpret its contents.
+
 ### Members Base
 
 ### Members Payments Processor