Deleting reference to README.security from docs

This change updates the documentation, requiring security concerns to
be provided in the 'Description' field of their README.chromium instead
of in README.security files.

Minor change to some of the wording, emphasising the importance of communicating security concerns in the Description for the benefit of security reviewers, but also other users of the dependency.


Bug: 383906216
Change-Id: I5a3465dd08afa503c794fe27aa542d36e8a15b3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6107858
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Jordan Brown <rop@google.com>
Cr-Commit-Position: refs/heads/main@{#1399680}

docs/adding_to_third_party.md

@@ -325,11 +325,10 @@ Non-Googlers can email one of the people in
 * Make sure you have the approval from Chrome ATLs as mentioned
   [above](#before-you-start).
 * Get security@chromium.org (or chrome-security@google.com, Google-only)
-  approval. Email the list with relevant details and a link to the CL.
-  Third party code is a hot spot for security vulnerabilities.
-  When adding a new package that could potentially carry security risk, make
-  sure to highlight risk to security@chromium.org. You may be asked to add
-  a README.security or, in dangerous cases, README.SECURITY.URGENTLY file.
+  approval. Document all security considerations, concerns, and risks in the
+  `Description:` field of the README.chromium. Third party code is a hot spot
+  for security vulnerabilities. Help people make informed decisions about
+  relying on this package by highlighting security considerations.
 * Add chromium-third-party@google.com as a reviewer on your change. This
   will trigger an automatic round-robin assignment to a reviewer who will check
   licensing matters. These reviewers may not be able to +1 a change so look for