Update README.md

[GloWE3]

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ethkey is a simple command-line tool for working with Ethereum keyfiles.

Usage

ethkey generate

Generate a new keyfile.
If you want to use an existing private key to use in the keyfile, it can be
specified by setting --privatekey with the location of the file containing the
private key.

ethkey inspect <keyfile>

Print various information about the keyfile.
Private key information can be printed by using the --private flag;
make sure to use this feature with great caution!

ethkey signmessage <keyfile> <message/file>

Sign the message with a keyfile.
It is possible to refer to a file containing the message.
To sign a message contained in a file, use the --msgfile flag.

ethkey verifymessage <address> <signature> <message/file>

Verify the signature of the message.
It is possible to refer to a file containing the message.
To sign a message contained in a file, use the --msgfile flag.

ethkey changepassword <keyfile>

Change the password of a keyfile.
use the --newpasswordfile to point to the new password file.

Passwords

For every command that uses a keyfile, you will be prompted to provide the
password for decrypting the keyfile. To avoid this message, it is possible
to pass the password by using the --passwordfile flag pointing to a file that
contains the password.

JSON

In case you need to output the result in a JSON format, you shall use the --json flag.
method to generate the following output for the same type of code as the previous version