documentation: add diagrams explaining the different kprobes & maps

[alban]

tcptracer-bpf.c has:

• 7 bpf maps
• 7 bpf kprobes/kretprobes

PR #39 is adding 4 more bpf objects, so it is becoming more complex.

We could add diagrams directly in the repository, to explain:

1. how the different bpf objects interact with each other
2. how the perf map event ordering works (could reuse & improve slide 34)
3. how the "guess offset" mechanism work (slide 30)

[alban]

source