Add documentation

Author: axelf4

README.md

@@ -10,4 +10,4 @@ Vim plugin that removes trailing whitespace
 Achieved by maintaining a set of all edited lines with trailing whitespace,
 backed by a Splay tree where children store line number offsets.
 
-*Vim support: requires Vim 8.2+*
+*Vim support: requires Vim 8.2+ or Neovim 0.5+*

doc/strip_trailing_whitespace.vim

@@ -0,0 +1,30 @@
+*strip_trailing_whitespace.txt*	For Vim version 8.2
+
+Removes trailing whitespace from modified lines on save.
+
+Some filetypes have significant trailing whitespace. An autocommand is
+defined in the "strip_trailing_whitespace_filetype" group that sets
+|b:strip_trailing_whitespace_enabled| to "0" for Markdown and diff files, and
+"1" for other filetypes. To disable: >
+    autocmd! strip_trailing_whitespace_filetype
+
+==============================================================================
+
+						*:StripTrailingWhitespace*
+:[range]StripTrailingWhitespace
+		Remove trailing whitespace from [range] lines (default all
+		lines).
+
+					*b:strip_trailing_whitespace_enabled*
+b:strip_trailing_whitespace_enabled
+		Per-buffer boolean toggle.
+
+					*g:strip_trailing_whitespace_max_lines*
+g:strip_trailing_whitespace_max_lines
+		Maximum number of modified lines with trailing whitespace to
+		keep track of before falling back to stripping the entire
+		file.
+		The default ensures the recursion depth limit won't be hit.
+
+
+ vim:tw=78:ts=8:noet:ft=help:norl: