Add SQLite3 databases to gitignore
Add README entries for charset conversion

Because IRC character encodings are not standardized, and Go strings are
UTF-8 by default, the stargazer bot would probably behave poorly on any
channel that used an incompatible encoding (for example, I've heard that
Japanese channels often use Shift_JIS).

These libraries provide Go character encoding conversion, which could be
incorporated into the bot for future improvements to handle those other
encodings gracefully.