Update to list Distros module in the manual (#6493)

doc/lib.rst

@@ -64,7 +64,6 @@ Core
 * `cpuinfo <cpuinfo.html>`_
   This module implements procs to determine the number of CPUs / cores.
 
-
 Collections and algorithms
 --------------------------
 
@@ -182,6 +181,12 @@ Generic Operating System Services
   This module implements asynchronous file reading and writing using
   ``asyncdispatch``.
 
+* `distros <distros.html>`_
+  This module implements the basics for OS distribution ("distro") detection and the OS's native package manager.
+  Its primary purpose is to produce output for Nimble packages, but it also contains the widely used **Distribution** enum
+  that is useful for writing platform specific code.
+
+
 Math libraries
 --------------