Update in readme info on new default linker and old debian releases

[mladedav]

• lld linker is now the default so I tried to make it clearer that people have to add the configuration for flamegraphs to work proprely without explicitly setting the linker.
• bullseye is not stable, it's even past its EOL now and in another 5 months it will be past its extended EOL. Personally, I would probably just remove the note altogether, but I didn't want to do that on my own since people could conceivably still use it so it you want me to, I'll delete it, otherwise I'm just removing the stable/testing notes about bullseye and bookworm.

[djc]

Good stuff, thanks!

[djc]

• Personally, I would probably just remove the note altogether, but I didn't want to do that on my own since people could conceivably still use it so it you want me to, I'll delete it, otherwise I'm just removing the stable/testing notes about bullseye and bookworm.

Happy for any further updates here that you think make sense!