Docs: Clarify that we don't modify the original list

Fixes #231

README.md

@@ -111,7 +111,7 @@ Functions returning a sublist of the original list.
 ### List to list
 
 
-Bag of various functions which modify input list.
+Functions returning a modified copy of the input list.
 
 * [-keep](#-keep-fn-list) `(fn list)`
 * [-concat](#-concat-rest-lists) `(&rest lists)`

dash.info

@@ -544,7 +544,7 @@ File: dash.info,  Node: List to list,  Next: Reductions,  Prev: Sublist selectio
 2.3 List to list
 ================
 
-Bag of various functions which modify input list.
+Functions returning a modified copy of the input list.
 
  -- Function: -keep (fn list)
      Return a new list of the non-nil results of applying FN to the

dash.texi

@@ -777,7 +777,7 @@ See also: @code{-select-columns} (@pxref{-select-columns}), @code{-select-by-ind
 @section List to list
 
 
-Bag of various functions which modify input list.
+Functions returning a modified copy of the input list.
 
 
 @anchor{-keep}

dev/examples.el

@@ -208,7 +208,7 @@ new list."
     (-select-column 1 '((1 2 3) (a b c) (:a :b :c))) => '(2 b :b)))
 
 (def-example-group "List to list"
-  "Bag of various functions which modify input list."
+  "Functions returning a modified copy of the input list."
 
   (defexamples -keep
     (-keep 'cdr '((1 2 3) (4 5) (6))) => '((2 3) (5))