Add cheatsheets (lsof, netstat, nmap, pdftk, ps, sam2p [new])

Add cheatsheets to the following modules:
* lsof
* netstat
* nmap
* pdftk
* ps

Added new module: `sam2p` (similar to pdftk)

Added a troubleshooting section to the README.md (python 2.6 doesn't comes with the argparse module)