Adds script to discover identifiers missing from Appsflyer's public sheet

[mattsilber]

I figure this PR depends on the result of the conversation related to this issue, but this adds scripts/Appsflyer/scrape_appsflyer.py to generate readme entries from the public Appsflyer SKAdNetworkIdentifiers sheet (minus URLs and descriptions).

Generated output on 9/14/2020:

Found 25 networks, 23 require addition.
Networks requiring readme addition:
|[aarki]()|4fzdc2evr5||
|[adcolony]()|4pfyvq9l8r||
|[adperio]()|vcra2ehyfk||
|[applovin]()|ludvb6z3bs||
|[crossinstall]()|prcb7njmu6||
|[curatemobileltd]()|52fl2v3hgk||
|[feedmob]()|fz2k2k5tej||
|[ironsource]()|su67r6k2v3||
|[lemmonetmobile]()|au67k4efj4||
|[lifestreet]()|t38b2kh725||
|[liftoff]()|7ug5zh24hu||
|[mintegral]()|kbd757ywx3||
|[mobrain]()|5ghnmfs3dh||
|[moloco]()|vcra2ehyfk||
|[pubnative]()|tl55sbb4fm||
|[remerge]()|2u9pt9hc89||
|[smartnewsads]()|9wsyqb3ku7||
|[spotad]()|f73kdq92p3||
|[startapp]()|5l3tpt7t6e||
|[tapjoy]()|ecpz2srf59||
|[thetradedesk]()|uw77j35x4d||
|[unicorn]()|578prtvx9j||
|[unityads]()|4dzt52r2t5||

[dynamix]

That is pretty useful! After AF has resolve the casing issue, I'll merge it. Having a link to the companies page and a descriptions would be nice thought. I'll write them and see if they could add that to the doc.

[mattsilber]

Thanks! It's definitely worth noting that it's incorrectly listing some duplicates (like: aarki 4FZDC2EVR5 | 4fzdc2evr5) due to that case-sensitivity issue. I've been getting so many mixed messages about that, it was too scary to enforce without confirmation