docs(en): Increase RAM requirement for en (#205)

# What ❔

Increase RAM requirements for External Node

## Why ❔

We have evidence that our tree requires more than 32 GB of RAM.

## Checklist

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- [ ] PR title corresponds to the body of PR (we generate changelog
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- [ ] Tests for the changes have been added / updated.
- [ ] Documentation comments have been added / updated.
- [ ] Code has been formatted via `zk fmt` and `zk lint`.

docs/external-node/03_running.md

@@ -8,7 +8,7 @@ This section assumes that you have prepared a configuration file as described on
 This configuration is approximate, expect updates to these specs.
 
 - 32-core CPU
-- 32GB RAM
+- 64GB RAM
 - SSD storage:
   - Testnet - ~800 GB (at the time of writing) and will grow over time, so should be constantly monitored
   - Mainnet - ~400 GB (at the time of writing) and will grow over time, so should be constantly monitored