CONTRIBUTING: Lead off with the security section

This reduces the chances that a skimmer reads "Issues are used for
bugs..." and files an issue without scrolling down to see the security
section.

I've also added links back to the security section from the all other
paragraphs that suggest using other channels (issues, pull requests,
IRC), so that no matter which anchor a skimmer starts at, they cannot
miss the fact that we have a special disclosure procedure for security
issues.  If we are confident that readers interested in submitting a
security issue will not start at a mid-document anchor without reading
the beginning of this file, we could drop some or all of these
back-refs.

Also adjust the lines I touch to use one line per sentence, since
that's the standard in other OCI Projects (like the runtime spec [1]).

[1]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/style.md#one-sentence-per-line

Signed-off-by: W. Trevor King <[email protected]>

CONTRIBUTING.md

@@ -1,14 +1,20 @@
 # Contribution Guidelines
 
-Development happens on GitHub.
-Issues are used for bugs and actionable items and longer discussions can happen on the [mailing list](#mailing-list).
+## Security issues
 
-The content of this repository is licensed under the [Apache License, Version 2.0](LICENSE).
+If you are reporting a security issue, *do not* create an issue or file a pull request on GitHub.
+Instead, disclose the issue responsibly by sending an email to [[email protected]](mailto:[email protected]) (which is inhabited only by the maintainers of the various OCI projects).
 
 ## Code of Conduct
 
 Participation in the Open Container community is governed by [Open Container Code of Conduct][code-of-conduct].
 
+## Discussion
+
+Development happens on GitHub.
+Issues are used for non-security bugs and actionable items; longer discussions can happen on the [mailing list](#mailing-list).
+Responsible disclosure for security issues is discussed [above](#security-issues).
+
 ## Meetings
 
 The contributors and maintainers of all OCI projects have monthly meetings at 2:00 PM (USA Pacific) on the first Wednesday of every month.
@@ -20,25 +26,24 @@ Minutes from past meetings are archived [here][minutes].
 ## Mailing list
 
 You can subscribe and browse the mailing list on [Google Groups][mailing-list].
+Responsible disclosure for security issues is discussed [above](#security-issues).
 
 ## IRC
 
-OCI discussion happens on #opencontainers on [Freenode][] ([logs][irc-logs]).
+Non-security OCI discussion happens on #opencontainers on [Freenode][] ([logs][irc-logs]).
+Responsible disclosure for security issues is discussed [above](#security-issues).
 
 ## Git
 
-### Security issues
-
-If you are reporting a security issue, do not create an issue or file a pull
-request on GitHub. Instead, disclose the issue responsibly by sending an email
-to [email protected] (which is inhabited only by the maintainers of
-the various OCI projects).
+The content of this repository is licensed under the [Apache License, Version 2.0](LICENSE).
 
 ### Pull requests are always welcome
 
-We are always thrilled to receive pull requests, and do our best to
-process them as fast as possible. Not sure if that typo is worth a pull
-request? Do it! We will appreciate it.
+We are always thrilled to receive pull requests for non-security changes, and do our best to process them as fast as possible.
+Not sure if that typo is worth a pull request?
+Do it!
+We will appreciate it.
+Responsible disclosure for security issues is discussed [above](#security-issues).
 
 If your pull request is not accepted on the first try, don't be
 discouraged! If there's a problem with the implementation, hopefully you
@@ -51,8 +56,9 @@ incorporating a new feature.
 ### Conventions
 
 Fork the repo and make changes on your fork in a feature branch.
-For larger bugs and enhancements, consider filing a leader issue or mailing-list thread for discussion that is independent of the implementation.
+For larger non-security bugs and enhancements, consider filing a leader issue or mailing-list thread for discussion that is independent of the implementation.
 Small changes or changes that have been discussed on the [project mailing list](#mailing-list) may be submitted without a leader issue.
+Responsible disclosure for security issues is discussed [above](#security-issues).
 
 If the project has a test suite, submit unit tests for your changes. Take a
 look at existing tests for inspiration. Run the full test suite on your branch