Add tidy.md document

Test: make
Change-Id: Ic2198532be4135401faffdda34d0e108c57b241c
diff --git a/docs/OWNERS b/docs/OWNERS
index 45ec523..2d71271 100644
--- a/docs/OWNERS
+++ b/docs/OWNERS
@@ -1,2 +1,3 @@
 per-file map_files.md = danalbert@google.com, enh@google.com, jiyong@google.com
 per-file native_code_coverage.md = pirama@google.com, srhines@google.com, allenhair@google.com
+per-file tidy.md = chh@google.com, srhines@google.com