Complete the string type description

A few words were missing from the static reference that reads:

Strings are mostly used for naming things without having to rely on external ID databases. They are restricted to the printable subset of 7-bit ASCII, plus some escaped characters (see section on constants). So what can be done is basically use string constants as is, concatenate or splice them, and use them as keys.

The result can be checked by clicking on the View app button of the pipeline below, then inputting string in the search area and selecting the type result.