Add release notes for Sabre 0.7.0
# Release Notes
+## Changes in Sawtooth Sabre 0.7.0
+
+* Update the allowed family version to include 0.5, 0.6 and update the current
+ version to 1. This will allow the Sabre transaction processor to accept
+ transactions from 0.5, 0.6 and 1 versions of Sabre.
+
## Changes in Sawtooth Sabre 0.6.1
* Update the `cylinder` dependency of the Rust SDK and the CLI to version `0.2`
