Bootstrap StableHLO governance (#186)

Bootstraps StableHLO governance from the SIG OpenXLA charter:
https://github.com/tensorflow/community/blob/master/rfcs/20220713-sig-open-xla.md.

In a follow-up pull request, I'll propose a process by which we'll be reviewing
StableHLO RFCs: https://github.com/openxla/stablehlo/labels/RFC.

docs/governance.md

@@ -0,0 +1,15 @@
+# StableHLO Governance
+
+## Future governance
+
+We aim to establish an open governance model drawing from standards such as
+LLVM, with particular emphasis on open design/roadmap discussions, public
+process for gaining technical steering rights, and OSS-first docs & repo
+governance (e.g. location, CLA, etc), repo location.
+
+## Near-term governance
+
+During the bootstrapping phase of the project in 2022, Google engineers will
+assume responsibility for the technical leadership of the project. It is a high
+priority to create a path for community members to take on technical
+leadership roles.