Fix errors in README and Documentation for adding a new token

[MantisClone]

Problem

README and Documentation is missing the following information required when adding new tokens to the token list:

• The hash is the token address for ERC20s or a hash calculated by the function linked below for native tokens.
• The network is the network name.
• The type is the currency type.

The full list of network names can be found in our SDK source code here: https://github.com/RequestNetwork/requestNetwork/blob/bae9bfd0fefb58c7df6a7005fe35d899aff64900/packages/types/src/currency-types.ts#L3-L36

The full list of currency types can be found in our SDK soucre code here: https://github.com/RequestNetwork/requestNetwork/blob/bae9bfd0fefb58c7df6a7005fe35d899aff64900/packages/types/src/request-logic-types.ts#L299-L312

For native tokens, the hash is calculated using this function: https://github.com/RequestNetwork/requestNetwork/blob/bae9bfd0fefb58c7df6a7005fe35d899aff64900/packages/currency/src/getHash.ts#L4-L16

Definition of Done

• Fix README
• FIx Documentation (requires CR in Gitbook)