make redirects

[drammock]

After #41 is finished & merged, we can/should stop hosting information in 2 places. Let's make the following redirects:

• https://phoible.github.io/ → https://phoible.org/
• https://phoible.github.io/conventions/ → https://phoible.org/conventions
• https://phoible.github.io/faq/ → https://phoible.org/faq