docs(osint): add TGScope to Telegram & Messaging Intelligence

[Courier-Britva]

Adds one line to Telegram & Messaging Intelligence in offensive-osint: TGScope, a free search engine over 3M+ public Telegram channels with three checks that are useful in recon:

• Creation date — dates a channel or supergroup from its numeric ID (Telegram issues IDs from rotating blocks since 2017), which exposes renamed or impersonating channels. Method and validation: https://tgscope.io/rnd/telegram-channel-id-clock
• Ad network — lists other channels that print the same advertising contact, i.e. channels sold or run together.
• Real reach — share of subscribers who actually see posts, to spot inflated audiences.

No account needed. Cited per the contributing guide; the ID method is documented in the linked research.

Disclosure: I run TGScope.