Update README.md

Add info about the dependencies

Especially the permit feature is... complex to say the least. Not guessable from the function signature alone probably, good idea to look at the test.

Author: jtakalai

README.md

@@ -66,3 +66,16 @@ Explanations of the origins and intents of all code found in DATAv2.sol:
 | 16...46 | Adapted from @openzeppelin/contracts/token/ERC20/presets/ERC20PresetMinterPauser.sol to implement the minting feature. The AccessControl.sol is a bit of a can of worms when it comes to state-space: the "role admin" can set up any constellation of roles and grant those roles and their administration to anyone; its implementation is quite elegant though, so it didn't feel very significantly worse than a "brute" `mapping (address => bool) isMinter` type of implementation, especially since it's all library code. Added isMinter convenience function. |
 | 48...74 | Adapted from LINK token to implement the ERC-677 token transfer hook. Recipient smart contracts can now react to DATAv2 token transfer which makes approve+transferFrom two-transaction flow avoidable if not entirely redundant. Decided to go for the simply ERC-677 instead of the ERC-777 because of some misfeatures on ERC-777 (defaultOperators, higher plain transfer gas price) as well as uncertain adoption at this stage. |
 | 76...103 | Allow the admin to change token symbol and name just in case, e.g. to support token rebranding, and graceful end-of-life after the possible next migration |
+
+## Dependencies
+
+* [`@openzeppelin/contracts/token/ERC20/extensions/draft-ERC20Permit.sol`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.0/contracts/token/ERC20/extensions/draft-ERC20Permit.sol)
+  * Allows a smart contract to spend tokens using a signature from the token holder
+  * For usage, see [`draft-ERC20Permit.test.js`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/test/token/ERC20/extensions/draft-ERC20Permit.test.js) in `openzeppelin-contracts`
+* [`@openzeppelin/contracts/access/AccessControl.sol`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.0/contracts/access/AccessControl.sol)
+  * Role-based access control (RBAC) where each role has another role as role-admin that can grant it
+  * DATAv2 has a _minter_ role as well as the _default_ role that manages it.
+  * [Tests also in the openzeppelin-contracts repo](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/test/access/AccessControl.behavior.js)
+* [`@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.0/contracts/token/ERC20/extensions/ERC20Burnable.sol)
+  * Unlocks the simple burning functionality in the OpenZeppelin ERC20.sol
+  * Emits transfer to zero address: [`emit Transfer(account, address(0), amount);`](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.0/contracts/token/ERC20/ERC20.sol#L264)