doc: align NetBSD build guide with BGL naming

[mawxcodehub]

Summary

• Updates the NetBSD build guide to use BGL/BGL Core naming instead of stale Bitcoin Core references.
• Keeps the documented commands and dependency instructions unchanged.

Validation

• git diff --check -- doc/build-netbsd.md
• rg -n "Bitcoin|bitcoind|bitcoin-cli|Bitcoin Core|Bitcoin repository|Bitcoin-Qt|bitcoin-qt" doc/build-netbsd.md returns no matches

Related to #32.

[MyTH-zyxeon]

Maintainer-facing review assist for #32/#39 triage:

This looks like a narrow docs-only BGL naming cleanup in doc/build-netbsd.md: it replaces stale Bitcoin Core / bitcoind wording with BGL Core / BGLd while leaving the actual NetBSD package and build commands unchanged. That seems aligned with the bounty-hunt documentation/comment cleanup category, but it is small enough that it should probably be classified explicitly under the docs/comment-edit payout bucket rather than treated like a larger code fix.

Before merge, I would check two acceptance details:

• Confirm BGLd is the preferred daemon spelling in user-facing NetBSD docs, since the patch changes prose but not command examples.
• Render the Markdown or do a quick docs preview to make sure the renamed intro/setup text still reads consistently next to the unchanged clone/configure commands.

No code-path or dependency risk jumps out from the diff; the main merge decision is payout/scope classification plus final naming consistency.