docs: Fixed faucet links

[kaustubhkapatral]

This PR fixes the faucet url and points them to the studio portal

[fraseragain]

This fixes the dead link, thanks. One suggestion: the line now points at the Studio home page, so a node operator will not know where the faucet is or that it needs an account. Something like this would be clearer, matching the wording in product-docs #78:

2. Acquire testnet CHEQ tokens through the testnet faucet in cheqd Studio (Account > Balances & Faucet). It needs a Studio account on a Basic or Build plan (there is a one-month free trial).

Also, the old faucet at testnet-faucet.cheqd.io is now behind Cloudflare Access, so nothing else in this repo should still link to it. I searched this repo and the README line is the only mention.