The Collaborative International Dictionary of English v.0.48:

Readable \Read"a*ble\ (r[=e]d"[.a]*b'l), a.
   Such as can be read; legible; fit or suitable to be read;
   worth reading; interesting. -- Read"a*ble*ness, n. --
   Read"a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

readably
    adv 1: in a legible manner; "you must write legibly" [syn:
           legibly, decipherably, readably] [ant: illegibly,
           undecipherably, unreadably]