Add SIG Autoscaling charter

This adds the SIG charter for SIG Autoscaling.

sig-autoscaling/charter.md

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+# SIG Autoscaling Charter
+
+This charter adheres to the conventions described in the [Kubernetes Charter README] and uses
+the Roles and Organization Management outlined in [sig-governance].
+
+## Scope
+
+Covers development and maintenance of components for automated scaling in
+Kubernetes.  This includes automated vertical and horizontal pod
+autoscaling, initial resource estimation, cluster-proportional system
+component autoscaling, and autoscaling of Kubernetes clusters themselves.
+
+### In scope
+
+- Autoscaling-related API objects, such as the HorizontalPodAutoscaler and
+  VerticalPodAutoscaler
+
+- Autoscaling-related tools, such as the cluster autoscaler,
+  single-component scaling tools (e.g. pod-nanny), and
+  cluster-proportional scaling tools
+
+- Ensuring API interfaces (the scale subresource) are availble and usable
+  to enable other SIG to write autoscalable objects, and enable people to
+  interact with those interfaces.
+
+[Link to SIG section in sigs.yaml][sigs.yaml]
+
+#### Code, Binaries and Services
+
+- Components and utilities that take automated action to scale a component
+  on the cluster
+
+- Components and utilities that take automated action to scale the cluster
+  itself
+
+- Special parts of client-go for interacting with with the scaling
+  interfaces used by the HPA (e.g. the polymorphic scale client).
+
+#### Cross-cutting and Externally Facing Processes
+
+- Reviewing implementations of the scale subresource to ensure that
+  autoscaling behaves properly
+
+- Coordinating with SIG Instrumentation to ensure that metrics APIs are
+  suitable for autoscaling on.
+
+- Coordinating with SIG Scheduling to make sure scheduling descisions can
+  interact well with the cluster autoscaler
+
+### Out of scope
+
+- Testing general cluster performance at scale (this falls under the
+  purview of [SIG Scalability]).
+
+- Owning metrics APIs (this falls under the purview of [SIG
+  Instrumentation].  SIG Autoscaling should collaborate with [SIG
+  Instrumentation] to ensure that metrics APIs are suitable for using in
+  autoscaling.
+
+## Roles and Organization Management
+
+This sig follows adheres to the Roles and Organization Management outlined in [sig-governance]
+and opts-in to updates and modifications to [sig-governance].
+
+### Deviations from [sig-governance]
+
+- SIG Autoscaling does not have chairs as a separate entity from tech
+  leads.  The tech leads have the responsibility of chairs.
+
+### Subproject Creation
+
+SIG Technical Leads
+
+[sig-governance]: https://github.com/kubernetes/community/blob/master/committee-steering/governance/sig-governance.md
+[sigs.yaml]: https://github.com/kubernetes/community/blob/master/sigs.yaml#L305
+[Kubernetes Charter README]: https://github.com/kubernetes/community/blob/master/committee-steering/governance/README.md
+[SIG Scalability]: https://github.com/kubernetes/community/blob/master/sig-scalability
+[SIG Instrumentation]: https://github.com/kubernetes/community/blob/master/sig-instrumentation