[Skip CI] Note first P2WPKH blocks
Resolves:
MODIFY
MagicalCryptoWallet.Backend/README.md
MagicalCryptoWallet.Backend/README.md
### POST filters
- At initial syncronization the wallet must specify the hash of the first block that contains native segwit output. This hash must be hard coded into the client. (ToDo: find the hash.)
+ At initial syncronization the wallet must specify the hash of the first block that contains native segwit output. This hash must be hard coded into the client.
+ - First block with P2WPKH: dfcec48bb8491856c353306ab5febeb7e99e4d783eedf3de98f3ee0812b92bad
+ - First block with P2WPKH on TestNet: b29fbe96bf737000f8e3536e9b4681a01b1ca6be3ac4bd1f8269cdbd465e6700
+
Filters are Golomb Rice filters of all the input and output native segregated witness `scriptPubKeys`. Thus wallets using this API can only handle `p2wpkh` scripts, therefore `p2pkh`, `p2sh`, `p2sh` over `p2wph` scripts are not supported. This restriction significantly lowers the size of the `FilterTable`, with that speeds up the wallet.
When a client acquires a filter, it checks against its own keys and downloads the needed blocks from the Bitcoin P2P network, if needed.

[Skip CI] Note first P2WPKH blocks

Resolves: https://github.com/nopara73/MagicalCryptoWallet/issues/20