[PATCH] Add a stub CONTRIBUTING.md pointing to the wiki

["Cole" <crobinso@redhat.com>]

Googling for 'edk2 pull request' did not find this wiki page:

https://github.com/tianocore/tianocore.github.io/wiki/EDK-II-Development-Process

Add it to CONTRIBUTING.md for more discoverability

Signed-off-by: Cole Robinson <crobinso@redhat.com>
---
I tried submitting a PR to edk2: https://github.com/tianocore/edk2/pull/854

It was auto closed with: `All checks passed. Auto close personal build.`

That confused me quite a bit. I could not understand what it was trying
to say. I looked at other successfully merged PRs, noticed some hits
about a 'push' label, but on looking to resubmit the PR it didn't seem
like I had permission to set labels. Googling did not turn up any explanatory
hits in the first two pages either. Eventually Laszlo pointed me in the
right direction though

A couple other suggestions to avoid that confusion

* Extend the mergify message to clarify PRs are largely only meant for
  maintainers to use. Maybe point at the wiki page or CONTRIBUTING.md

* Add a github new PR template with a comment giving more explanation:
https://docs.github.com/en/github/building-a-strong-community/creating-a-pull-request-template-for-your-repository

 CONTRIBUTING.md | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 CONTRIBUTING.md

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000000..212c69ce8b
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,3 @@
+# Contributing to EDK2
+
+Contributor documentation is maintained on the wiki: https://github.com/tianocore/tianocore.github.io/wiki/EDK-II-Development-Process
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2.26.2