Update runtime files.

runtime/doc/if_pyth.txt

@@ -81,6 +81,18 @@ Examples:
 >
 	:pydo return "%s\t%d" % (line[::-1], len(line))
 	:pydo if line: return "%4d: %s" % (linenr, line)
+<
+One can use `:pydo` in possible conjunction with `:py` to filter a range using
+python. For example: >
+
+	:py3 << EOF
+	needle = vim.eval('@a')
+	replacement = vim.eval('@b')
+
+	def py_vim_string_replace(str):
+		return str.replace(needle, replacement)
+	EOF
+	:'<,'>py3do return py_vim_string_replace(line)
 <
 							*:pyfile* *:pyf*
 :[range]pyf[ile] {file}