Improve signing and checksumming of release assets about wordfence-cli

[davidnuzik]

v2.0.1-rc5 10/30/2023

SUMMARY:
QA validation PASSED.
Single checksum file now, and docs change looks good!

VALIDATION STEPS

1. Refer to docs/Installation.md (note that this links to voodoo-child branch since we haven't merged to mainline yet) and follow the "Verifying the Authenticity of a Release Asset" section.
2. Per the documentation, obtain the public GPG key and import it. (Optionally sign it with your private key).
3. Download the checksums.txt release asset (rc5) and checksums.txt.asc. Verify checksums.txt using checksums.txt.asc
4. When verify, ensure get output that is similar to the example in the Installation.md doc.
5. Download each asset, verify each via sha256sum e.g. within the directory containing all assets including checksums files, run sha256sum --ignore-missing -c checksums.txt and get an "OK" for each.

sha256sum --ignore-missing -c checksums.txt
wordfence_amd64.tar.gz: OK
wordfence_arm64.tar.gz: OK
wordfence.deb: OK
wordfence-2.0.1rc5-py3-none-any.whl: OK
wordfence-2.0.1rc5.tar.gz: OK

NOTES:
BEFORE the change (RC4 pictured)

AFTER the change (RC5 pictured)