Add module level docs for Seg/Node path modules

Author: harendra-kumar

core/src/Streamly/FileSystem/Path/Node.hs

@@ -5,6 +5,13 @@
 -- Maintainer  : [email protected]
 -- Portability : GHC
 --
+-- Represent 'File' or 'Dir' type path nodes explicitly as separate types for
+-- the safety of path append operation. A 'Dir' path is a branching or
+-- intermediate node whereas a 'File' type is a terminal or leaf node. We
+-- cannot append a path to a 'File' type path.
+--
+-- See the overview in the "Streamly.FileSystem.Path" module for more details.
+--
 module Streamly.FileSystem.Path.Node
     (
     -- * Types

core/src/Streamly/FileSystem/Path/Seg.hs

@@ -5,6 +5,13 @@
 -- Maintainer  : [email protected]
 -- Portability : GHC
 --
+-- Represent 'Rooted' or 'Branch' type path segments explicitly as separate
+-- types for the safety of path append operation. A Rooted path is an absolute
+-- path or a path that is relative to the current directory with a leading dot.
+-- Rooted paths cannot be appended to other paths.
+--
+-- See the overview in the "Streamly.FileSystem.Path" module for more details.
+--
 module Streamly.FileSystem.Path.Seg
     (
     -- * Types

core/src/Streamly/FileSystem/Path/SegNode.hs

@@ -5,6 +5,13 @@
 -- Maintainer  : [email protected]
 -- Portability : GHC
 --
+-- Use 'Rooted' or 'Branch' path segment type annotations as well as 'File' and
+-- 'Dir' node type annotations on the same path for the safety of path append
+-- operation. A Rooted path cannot be appended to other paths, and you canno
+-- append a path to a 'File' type path.
+--
+-- See the overview in the "Streamly.FileSystem.Path" module for more details.
+--
 
 module Streamly.FileSystem.Path.SegNode
     (