doc: use BGL terms in NetBSD guide

[pinehill99]

Bounty/improvement route: #39 / #81

Summary

• Align the NetBSD build guide with Bitgesell naming.
• Replace remaining inherited Bitcoin Core / bitcoind wording in doc/build-netbsd.md with BGL Core / BGLd / Bitgesell terms.

Validation

• rg -n "Bitcoin Core|bitcoind|bitcoin-cli|bitcoin-qt|bitcoin.conf" doc/build-netbsd.md returned no matches after the patch.
• git diff --check
• git diff --check HEAD~1..HEAD

AI-assisted with OpenAI Codex; I reviewed the diff and validation output before submitting.

[MyTH-zyxeon]

Maintainers - this looks like a narrow #81 documentation cleanup candidate that should be easy to review without dragging in runtime risk.

Why it seems reasonable:

• Scope is one file only: doc/build-netbsd.md.
• The diff is terminology alignment (bitcoind / Bitcoin Core -> BGLd / Bitgesell / BGL Core) rather than consensus, wallet, RPC, or build-logic changes.
• mergeStateStatus=CLEAN and mergeable=MERGEABLE from the public metadata, with no visible prior PR discussion when checked from my side.

Suggested acceptance checks:

1. Confirm every renamed binary/project term now matches the actual NetBSD build output and packaging names used in this repo.
2. Confirm no nearby commands in the guide still reference upstream-only Bitcoin names, so the document does not end up half-converted.
3. Because #81 explicitly says comment/README cleanups can be useful but should pay less than substantial test/CI/code fixes, confirm whether this falls into that lower-tier documentation bucket.

If you want contributors to prioritize higher-signal #81 work next, calling that out here after merge/review would help route future small PRs away from duplicate docs-only churn.