add r2ghidra

[n01e0]

Added r2ghidra.
There is already a ghidra, but there are subtle differences in output, so it would be interesting to compare the two.

[mborgerson]

Is r2ghidra being worked on and are the results much different/better than Ghidra? I'm not sure it's worth maintaining here if it's basically just Ghidra's decompiler in a different package

[n01e0]

That is certainly a difficult point.
Since r2ghidra is based on the Ghidra decompiler, it is basically the same, with some differences.
I'm not sure if there is any benefit other than comparing the output of Ghidra and r2ghidra out of complete curiosity.
I don't think there is much need for it, but since I don't know what the demand is, I'll leave it to you to decide.