[FEAT] Update ctl docs so it's clearer how phonetic columns work

[afua-moj]

Is your proposal related to a problem?

I was just writing up an issue, to request that we can have a phonetic_fullname_col_name in the ctl.forenameSurnameComparison and realised when looking at the code that this is done automatically if you include phonetic_forename_col_name and phonetic_surname_col_name.

In the docs it says "Including this parameter will create an exact match level for phonetic_surname_col_name" which doesn't capture everything the code says.

Describe the solution you'd like

Small update to the doc to make this functionality clear. If

phonetic_forename_col_name (str, optional): The name of the column with
                phonetic reduction (such as dmetaphone) of forename_col_name. Including
                parameter along with `phonetic_surname_col_name` will create an exact match level for
                "Full name phonetic match".
                Defaults to None