Add examples for walletdb usage.
Add examples for walletdb usage.

Roasbeef/btcwallet,decred/dcrwallet,jrick/btcwallet,synrg-labs/btcwallet,jrick/dcrwallet,jrick/btcwallet,Stash-Crypto/btcwallet,Roasbeef/btcwallet,decred/dcrwallet,btcsuite/btcwallet,jrick/dcrwallet,Stash-Crypto/btcwallet,synrg-labs/btcwallet,btcsuite/btcwallet