Offer to help with maintenance

[niklasf]

Hi, if you like, I'd be happy to help along the lines of https://github.com/rust-rocksdb/rust-rocksdb/blob/master/MAINTAINERSHIP.md, occasionally reviewing pull requests and triaging issues.

My main interest in RocksDB is due to lichess.org (another free open-source software project) using RocksDB as the backend for its chess opening explorer.