Add a link to syntax.md after error messages

* Example error messages from the upload validator:
    remote: ERROR: commit ...: syntax: OWNERS:3: ...
    remote: ERROR: commit ...: ignored: OWNERS:5: ...
    remote: ERROR: commit ...: unknown: xyz@g.com at OWNERS:2
    remote: ERROR: commit ...: See OWNERS file syntax document
    at https://gerrit.googlesource.com/.../syntax.md

Change-Id: I8f58e0237a5de542a82176187ea72e5ffd0cbee8
1 file changed
tree: 27cef00fa3a5bf808e07f5b3036374f7a2276ba8
  1. BUILD
  2. LICENSE
  3. OWNERS
  4. src/