Update docs

Author: penelopeysm

src/varname.jl

@@ -797,14 +797,14 @@ Specifically, suppose you have a custom index type `MyIndexType` and you want
 to be able to de/serialise a `VarName` containing this index type. You should
 then implement the following two methods:
 
-1. `AbstractPPL.index_to_dict(i::MyIndexType)` should return a dictionary
-   representation of the index `i`. This dictionary must contain the key
-   `"type"`, and the corresponding value must be a string that uniquely
+1. `AbstractPPL.index_to_dict(i::MyModule.MyIndexType)` should return a
+   dictionary representation of the index `i`. This dictionary must contain the
+   key `"type"`, and the corresponding value must be a string that uniquely
    identifies the index type. Generally, it makes sense to use the name of the
    type (perhaps prefixed with module qualifiers) as this value to avoid
    clashes. The remainder of the dictionary can have any structure you like.
 
-2. Suppose the value of `index_to_dict(i)["type"]` is "MyModule.MyIndexType".
+2. Suppose the value of `index_to_dict(i)["type"]` is `"MyModule.MyIndexType"`.
    You should then implement the corresponding method
    `AbstractPPL.dict_to_index(::Val{Symbol("MyModule.MyIndexType")}, dict)`,
    which should take the dictionary representation as the second argument and