Fix documentation associated with `query` parameter `q` being a string

[dgr]

Today, Etaoin's documentation states that when query is given a string for its q parameter, the string is interpreted as an XPath query. This is only partially true. In reality, the string is interpreted as either XPath or CSS, depending on the :locator associated with the driver. By default, drivers are initialized with :locator set to "xpath", but this may be changed using the use-css function and the with-css macro. In that case, the string is interpreted as a CSS formatted locator.

The documentation (both doc string for query as well as User Guide description of query's q parameter) should be corrected.

[lread]

Ok, PR welcome!