It already contains both the signature of the message and the SHA256sum of each binaries (as signed message).
You verify the signed hash file via gpg --verify sha256sum.txt.asc to see if it's legit.
After passing verification, open it using your notepad or text editor, then compare the SHA256sum of the binaries to the listed SHA256 hashes.
That's the only thing that works for me the result is below.
C:\Users\Admin\Downloads\Programs\New folder>gpg --verify sha256sum.txt.asc
gpg: Signature made 24/12/2018 4:16:07 pm Malay Peninsula Standard Time
gpg: using RSA key 8C5211764922589A
gpg: Good signature from "goatpig (Offline signing key for Armory releases)" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: 745D 707F BA53 968B DF63 AA8D 8C52 1176 4922 589A
gpg: WARNING: not a detached signature; file 'sha256sum.txt' was NOT verified!
I just trying to include the installer when verifying but it didn't work except on verifying only the sha256sum.txt.asc
So to make sure it's genuine I manually created the checksums with GpgEX and check the hash inside with the notepad and compared it to sha256sum.txt.asc the hash are the same so it's guinuine as I said on my previous suggestion above.