Add wiki content explaining higher level usage

As suggested by @phraktle in #150.

While TutorialTest explains how to use LmdbJava, it offers virtually no real guidance on the higher level options and trade-offs such as:

  • Is LMDB a good fit for your workload? (eg B-Tree, LSM, SQL, column formats, noSQL)
  • Buffer options in Java
  • Serialisation options
  • Keys, including comparators
  • Concurrency, including threads and multi-process
  • Storage efficiency
  • Bulk loading
  • Summary

It would be good to capture some of this in a wiki, especially so the community can edit it and share what they've found useful.