Add licensing caveat for BASPI, PIQ and TA forms (#199)

README.md

@@ -7,3 +7,8 @@ The short term goal for the schema is to encompass all of the requirements of th
 
 A parallel repository for this one has been created for the [Open API Specifications](https://github.com/Property-Data-Trust-Framework/api) for the data exchanges themselves, which will evolve independently.
 
+This repository is intended to be a living document, with the schema evolving over time as the requirements of the framework are refined and extended. The schema is versioned to allow for backwards compatibility and to enable the evolution of the schema over time.
+
+## Licensing
+The schema is licenced under the permissive [MIT License](https://opensource.org/license/MIT), but note that overlays and references are included which contain fields from [BASPI](https://homebuyingsellingcouncil.co.uk/wp-content/uploads/2021/03/Terms-of-Licence-mandatory-download-for-use-of-BASPI.pdf), [PIQ](https://www.propertymark.co.uk/static/14e7c154-98de-4230-957f09bd8d5ddeec/f542b10a-7710-4c37-b3958ccaeec25d4b/property-information-questionnaire-residential-sales.pdf) and [Law Society TA](https://www.lawsociety.org.uk/topics/property/transaction-forms) forms. If you intend to render data described by the schema into one of these forms, you should ensure that you comply with the terms of the respective licences.
+