Fix phonesky source issues, fix stock GMS returning on certain devices, add shell.nix, update README

[HPsaucii]

Fixes issue #73

[bioluks]

This really needs to be merged since the only other alternative option practically announced the death of the project - microg_installer_revived.

Newcomers should have a fully working alternative at least.

[recallmenot]

for anyone wondering where to get it now: Phonesky.apk.tar.gz conf/resdl-download.txt shows to put the apk in resdl/system/priv-app/Phonesky/ please verify sha1sum of .gz against virustotal

[HPsaucii]

for anyone wondering where to get it now: Phonesky.apk.tar.gz conf/resdl-download.txt shows to put the apk in resdl/system/priv-app/Phonesky/ please verify sha1sum of .gz against virustotal

You can get it from any source you want (i personally used nikgapps), and users can just put it in the root directory of the project under the name of Phonesky.apk, but yes, if you dont wanna use my fork or anything, that works too (my fork includes some fixes for certain devices aswell, so keep that in mind when deciding whether to use my fork or not :3)

[MugoSquero]

Does the Phonesky.apk file have to be legit/modified Play Store? Or can it be the MicroG Companion app?

[HPsaucii]

@MugoSquero It can be anything you want, but be warned that only a functional play store will be able to pass the basic integrity level of play integrity, due to play integrity relying on specific events that only the functional play store currently supplies