Adding guidance for addressing critical issues (#483)

* Adding guidance for addressing critical issues

* More details

* Addressing PR feedback

* Updating wording

* typo

contributions/opening-and-assessing-issues.md

@@ -109,6 +109,14 @@ GitHub [milestones](https://docs.github.com/en/issues/using-labels-and-milestone
 
 Before a new milestone can be created in the repository, the new milestone must be approved by the project Maintainers, following the decision making rules in the [GOVERNANCE.md](../GOVERNANCE.md) file.
 
-### GitHub project assignments
+## GitHub project assignments
 
 In place of assigning a milestone, consider assigning issues to a GitHub [project](https://docs.github.com/en/issues/planning-and-tracking-with-projects/learning-about-projects/about-projects). An issue can have multiple project assignments, and each Project Maintainer can manage their own GitHub projects and the priorities within those projects.
+
+## Critical priority issues
+
+Such a priority must be used sparingly and only applies to released package issues that severely impact a large number of users. For an issue to be deemed critical it must be severe enough to require the immediate attention of the Project Maintainers. Security and data loss bugs, while unlikely in MRTK, are examples of issues that may warrant critical status.
+
+High priority issues that aren't deemed critical should be addressed during scheduled Project Maintainer meetings. These meetings typically occur every two weeks.
+
+When a critical bug is discovered, the Project Maintainers must be contacted immediately, and the issue must be tagged with "Priority: Critical". All Project Maintainers must then meet as soon as possible to decide if the issue warrants a patch release. The Project Maintainers can use an agreed upon communication method, such as a group email or messaging platform, to arrange a meeting.