Added scapy on github/explore with scapy logo.

[joesinghh]

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests for Python2 and Python3 (using tox or, cd test && ./run_tests_py2, cd test && ./run_tests_py3)
• If the PR is still not finished, please create a Draft Pull Request

I added scapy on github explore with a logo as mentioned in #399 - easy.
I also added a link to the scapy topic in README.md.

here is the PR adding scapy topic to github/explore PR 2652

[guedou]

Thanks for submitting Scapy to github explore! It does not make much sense to update our README.

It will be better to add a reference to the Scapy topic in the MISC section of https://github.com/secdev/awesome-scapy

[joesinghh]

okay, I'll do that. Thank you.