no mention of gitian reproducible builds in verification guides

[plowsof]

e.g. in these guides
https://www.getmonero.org/resources/user-guides/verification-windows-beginner.html
https://www.getmonero.org/resources/user-guides/verification-allos-advanced.html

there is no mention of gitian reproducible hashes. and may seem that we 'trust' solely the signed hashes.txt list of hashes. when in reality it is the reproducible hashes of gitian that we trust (which bF signs after several other contributors have confirmed them)

here are the submissions for 0.18.3.3 linux binaries https://github.com/monero-project/gitian.sigs/tree/master/v0.18.3.3-linux

a short sentence or 2 describing gitian (soon to be guix) build process would suffice i think