Document ghidra usage

[il-steffen]

Document the flow for obtaining traces of one or more files and visualizing them in Ghidra:

• install ghidra and add ghidra_cov_analysis.py to scripts dir
• kafl_fuzz.py to create a corpus
• kafl_cov.py to create trace files
• ghidra_cov_analysis.sh to sort out unique found edges and return coverage report