add more linux instructions and fix + add to flatpak inst. building

[LackingCats]

Most of the popular linux distributions are already covered, however the niche ones should also be considered, and that is why I am making this pull request rn

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[LackingCats]

all done, all linux versions as seen on repology now appear on the linux.md download page!

[LackingCats]

pls squash thx

[LackingCats]

i should be all done, lmk if any changes need to be made

[LackingCats]

all ready for review :) lmk if i should just remove aosc/alt linux

[LackingCats]

so far i added a dropdown menu (see deploy preview)

[LackingCats]

hmm the dropdown is a little funny :/

[LackingCats]

Yayyy!!! Finally ready for review

[LackingCats]

Ready 4 review (again again)

[ZekeZDev]

assigning myself to look through thoroughly on my holidays. Apologies for very late review

[LackingCats]

ready for review (been a while huh)

[LackingCats]

just syncing (pls no lint fail)

[LackingCats]

ready for review

[LackingCats]

once again ready for review

[LackingCats]

also pls squash

[LackingCats]

(i'm not very efficient with my commits)