add rfc template

tsa/policy/template.mdwn

+[[!meta title="TPA-RFC-X: RFC template"]]
+
+Summary: this template describes the basic field a TPA-RFC policy
+should have. Refer to [[tpa-rfc-1-policy]] for the actual policy requirements.
+
+# Background
+
+# Proposal
+
+## Scope
+
+## ...
+
+# Examples
+
+Examples:
+
+ * ...
+
+Counter examples:
+
+ * ...
+
+# Deadline
+
+
+# Status
+
+This proposal is currently in the `draft` state.
+
+# References
+
+See [[tpa-rfc-1-policy]].