Add Readme to multichain-tools package

[Pessina]

Currently the package: https://github.com/near/multichain-tools, doesn't have any readme, it should contain:

• Description
• Installation
• How to use
• Examples

[benmalcom]

Hey @Pessina , nice job on the README, just a little formatting issue here (around typescriptCopy code).

Also, for the function parameters, I think it will be good to add their descriptions so the average person implementing can know what they're about.