message: add wallet_create_key doc
diff: @@ -358,6 +358,22 @@ This command will return the password that can be used to unlock the wallet in t
  PW5KFWYKqvt63d4iNvedfDEPVZL227D3RQ1zpVFzuUwhMAJmRAYyX
  ```
  +@subsection v1walletcreatekey wallet_create_key
  +
  +Creates a key within the specified wallet, wallet must be opened and unlocked.
  +Param are: 1.name of the wallet to create key in; 2. type of key to create, currently we support two values: K1 and R1
  +
  +@subsubsection examplewalletcreatekey Example wallet_create_key Usage
  +```
  +$ curl http://localhost:8888/v1/wallet/create_key -X POST -d '["default","K1"]'
  +```
  +
  +@subsubsection examplewalletcreatekeyresult Example wallet_create_key Result
  +This command will return the public key of the created key
  +```
  +EOS6GZE1xeo6jX2AtP2Z6WTcxawQMH7cyYMNpG6Q3q7s514zyRhgo
  +```
  +
  @subsection v1walletopen wallet_open
  Open an existing wallet of the given name
  