Update documentation

docs/src/index.md

@@ -53,11 +53,29 @@ for (k, v) in family
 end
 ```
 
-For a list of available identifiers see
+## Available keys and naming convention
+A list of available pseudopotential identifiers is available as
 ```@example index-example
 PseudoPotentialData.family_identifiers()
 ```
-More details on the meaning of these keys is given in the README of the
+
+The naming convention is as that each pseudo family name consists
+of a list of fields, which are concatenated using a `.` (dot).
+These are:
+1. An identifier for the pseudo family (like `dojo` for the [PseudoDojo](http://www.pseudo-dojo.org/) family of potentials.
+2. The type of pseudopotential (`nc`: norm-conserving, `us`: ultrasoft, `paw`: projected  augmented wave)
+3. Details on the level of relativistic effects employed when generating the pseudo (`fr`: Full relativistic, `sr`: Scalar relativistic, `nr`: No relativistic)
+4. The functional for which the pseudopotential was prepared
+5. The version of the pseudopotential construction (with version points replaced by underscores)
+6. The program used to generate the pseudopotential
+7. Some additional comments specifying the pseudopotential.
+   E.g. for PseudoDojo potentials there is usually a `stringent` version
+   (requiring slightly larger cutoffs) and a `standard` version being a bit softer.
+8. The format of the pseudopotential files in this library.
+
+More details on the meaning of these keys
+will be provided at a later stage.
+Some information is also available in the README of the
 [PseudoLibrary](https://github.com/JuliaMolSim/PseudoLibrary/blob/7c4b71a3b9d70a229d757aa6d546ef22b83a85a9/README.md)
 repository.