Update README.md

README.md

 # materials
 
-This is a small project to host material definitions to be used in a GDML Geometry simulation to be simulated with Geant4.
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+This is a small project to host material definitions to be used in a GDML Geometry simulation inside Geant4.
+
+The contents of this repository will be synchronized with the [following website](https://sultan.unizar.es/materials/).
+
+The main objective is to define material files with version traceability features that will be integrated with restG4 and TRestG4Metadata.
+To allow for this traceability we should define a reference string at the beginning of the materials file, 
+enclosed in a comment between the following identificative header `##VERSION ##`.
+
+It shoould include a line as the following line.
+```
+<!-- ##VERSION REST materials 1.0## -->
+```
+