Readme: Mention ToolsTreeProfiles=package-manager when building for another distribution

[cvlc12]

Use --defer-partitions-factory-reset yes
Requires systemd 259

Removed parts which are obsolete now when using sysinstall

[cvlc12]

See https://mastodon.social/@pid_eins/115740831317295811

This is indeed the same thing:

 [ user repart.d]$ grep Reset ./*.conf
./30-swap.conf:FactoryReset=yes
./40-root.conf:FactoryReset=yes
./50-home.conf:FactoryReset=yes

[cvlc12]

Also update the readme to reflect that when [Distribution] is needed, so is ToolsTreeProfiles=package-manager

[francoism90]

@cvlc12 In my PR I have added and adjust somethings in README.md: https://github.com/systemd/particleos/pull/131/changes#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5

I believe the last " for homectl update is wrong?

Maybe you could also add them + flatpak? :)

[cvlc12]

Updated to remove the parts related to systemd-repart to reflect #158

ToolsTreeProfiles should really be mentioned in the Readme.