doc: add docs for newlineafter flag

Provide documentation for --newlineafter flag Signed-off-by: John Cai <johncai86@gmail.com>

Author: john-cai

Documentation/pretty-options.txt

@@ -32,6 +32,10 @@ people using 80-column terminals.
 This is a shorthand for "--pretty=oneline --abbrev-commit"
 used together.
 
+--newlineafter[=(decorations)]
+Used in conjunction with --pretty=oneline to add a line break after
+decorations
+
 --encoding=<encoding>::
 Commit objects record the character encoding used for the log message
 in their encoding header; this option can be used to tell the