Revise `ReadSize` error message

[cjsha]

from here:

open-ephys/bonsai-onix1#498 (comment)

ReadSize must be a multiple of four but that is not stated anywhere even in the relevant error message.

[bparks13]

Instead of simply stating this error, the plugin should change the read size by increasing it to the next word boundary. This should be documented in the plugin documentation page.