Add guide for non-archive validator

Helps to reduce disk space:
https://wiki.polkadot.network/docs/ru/maintain-guides-how-to-validate-polkadot#synchronize-chain-data

1) Try sync a node with full node DB: https://s3-ap-southeast-1.amazonaws.com/cennznet-snapshots.centralityapp.com/azalea/1.2.2/fullnode/index.html
2) Restart with `--unsafe-pruning --pruning ` flags

iirc `NUM_BLOCKS` must be sufficiently large for validators to allow reorgs for grandpa in worst-case scenarios e.g. (5 * 12 * 60 * 24) would be enough for 1 day of reorgs

---
After trying the above process, this seems to sync well
```bash
docker run --restart=always -v $(pwd)/data:/data -p 9944:994 \
cennznet/cennznet:1.5.0 \
--chain=/cennznet/genesis/azalea.raw.json \
--unsafe-ws-external \
--validator \
--base-path=/data \
--unsafe-pruning \
--pruning 1000
```

DB usage:
`5.4G data/chains/CENNZnet Azalea V1`

Other validators showing around 90GB

Start with the linked Polkadot validator guide and the CENNZnet snapshot instructions in the issue. Add a wiki guide for running a non-archive validator using the documented Docker command and pruning settings, including the reorg consideration and expected disk usage; done means the process is clear enough to follow.

Written by the indexing model from the issue text.