adding readme for dhp-schema

dhp-schemas/README.md

@@ -1,3 +1,11 @@
 Description of the project
 --------------------------
-This project defines **serialization schemas** of Avro data store files that are used to pass data between workflow nodes in the system.
+This project defines **object schemas** of the OpenAIRE main entities and the relationships that intercur among them. 
+Namely it defines the model for 
+  
+-  **research product (result)** which subclasses in publication, dataset, other research product, software
+-  **data source** object describing the data provider (institutional repository, aggregators, cris systems)
+-  **organization** research bodies managing a data source or participating to a research project
+-  **project** research project
+ 
+Te serialization of such objects (data store files) are used to pass data between workflow nodes in the processing pipeline.