Update ppp.md

Add reference to including the PPP point's .h file to get the typedef for the callback, as well as adding instruction for adding PPP_PROT_REG_CB.
docs/record_replay: add link to PANDA Share

The documentation for record/replay was written before the launch of the PANDA Share. This commit updates the documentation with a link to the website.
Merge pull request #29 from yrp604/patch-4

Update ppp.md
Merge pull request #30 from tss/patch-1

docs/record_replay: add link to PANDA Share
Added tainted_branch plugin and assorted modifications to the taint syste to make it run