Document required disk space

[Kixunil]

First of all, this project looks really cool! I hope I will be able to play with it at some point. :) Maybe even package it into my deb repo at some point.

I'd like to know the system requirements, especially disk space and I think it'd be useful to have it in the README.

[sgeisler]

So far I can only report a lower bound of currently 740GB disk space used by postgres with the only DB being the indexer. Postgres itself reports a DB size of 692GB (either overhead or Gibi/Giga difference). I'll have to get a bigger SSD before continuing the test as my system partition is running full and I figured putting the DB on RAID6 with spinning disks won't do me any good either 😂

This will also give me the opportunity to compare the performance as my current setup (SATA SSD in software RAID1 encrypted and with LVM on top) seems rather slow, maxing out at 15k tx/s and taking days to build the indices. The bottleneck is definitely the DB/io.

[Kixunil]

@sgeisler thanks a lot for the report! Looks like I will have to get a big SSD before I play with it.