Populate governance document

Governance.md

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+# MotionMark Governance Policy
+
+MotionMark uses multistakeholder governance. This allows participating organizations to collaborate and
+develop the benchmark with the goal of maintaining and developing the benchmark to represent rendering-
+related workloads on the web. This also provides a structure that can endure to provide maintenance and
+adapt to the future web.
+
+An eligible “browser project” is a core end-to-end web browser engine with an integrated JavaScript engine
+which distributes implementations widely. The project may delegate decision making within MotionMark
+to multiple representatives (for example, to review code commits or to provide consensus for major changes).
+The participating browser projects at this time are [Blink](https://www.chromium.org/blink/),
+[Gecko](https://developer.mozilla.org/en-US/docs/Glossary/Gecko), and [WebKit](https://webkit.org).
+Additions to this list can be proposed via filing an issue in this GitHub repository, and additions to this
+list count as a Major change (described below).
+
+The intent is that the working team should be able to move quickly for most changes,
+with a higher level of process and consensus expected based on the impact of the change. The working team
+consists of the contributors to MotionMark, and their respective browser projects.
+
+-   **Trivial change** - This is a change that has no effect on the official benchmark and includes changes
+    to whitespaces, comments, documentation outside policies and governance model, and unofficial test cases.
+    A trivial change requires approval by a reviewer, who is not the author of the change,
+    from one of the participating browser projects. The current reviewership policies for the participating
+    browser projects can be found
+    [here](https://chromium.googlesource.com/chromium/src/+/master/docs/code_reviews.md),
+    [here](https://wiki.mozilla.org/Firefox/Code_Review), and
+    [here](https://webkit.org/commit-and-review-policy/).
+    The intent is to ensure basic code quality & license compatibility, not to reach agreement.
+    For example, one participating browser project might be both writing and reviewing a new benchmark in
+    a subfolder to test in their own CI, or reviewing code written by an external contributor.
+-   **Non-trivial change** - This is a change that has small impact on the official benchmark and includes
+    changes to official test cases, test runners, bug fixes, and the appearance of the benchmark.
+    A non-trivial change requires approval by at least two of the participating browser projects
+    (including either authoring or reviewing the change) and none other strongly opposed to the change
+    within 10 business days.
+-   **Major change** - This is a change that has major implications on the official benchmark such as
+    releasing of a new version of the benchmark or any revisions to governance policies and processes,
+    including changes to the participating browser projects.
+    A major change requires a consensus, meaning approvals by each of the participating browser projects.
+
+This governance policy and associated code will be hosted inside the MotionMark repository within
+the WebKit GitHub organization under the 2-clause BSD license.