Add a doc about `dex_preopt_check`.

The doc lists some possible causes of a `dex_preopt_check` error, which
can be useful for developers to understand how to debug the error.

Bug: 232542678
Test: m nothing
Change-Id: I2e9868a6a470e41e8c3743c045e0cf4cf7367efa
diff --git a/core/OWNERS b/core/OWNERS
index dae34ff..980186c 100644
--- a/core/OWNERS
+++ b/core/OWNERS
@@ -1,4 +1,4 @@
-per-file dex_preopt*.* = ngeoffray@google.com,skvadrik@google.com
+per-file *dex_preopt*.* = ngeoffray@google.com,skvadrik@google.com
 per-file verify_uses_libraries.sh = ngeoffray@google.com,skvadrik@google.com
 
 # For version updates