Adding nft example

.gitignore

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+node_modules
+
+#Hardhat files
+cache
+artifacts
+.env

README.md

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-# hardhat_polygon_nft
+# Hardhat-Polygon-Nft example
 An Nft example using hardhat and Polygon blockchain
+
+
+**Commands to create a new project using Hardhat**
+
+`mkdir hardhat-example3-nfts`
+`cd hardhat-example3-nfts`
+`npm init --yes`
+`npm install --save-dev hardhat`
+`npx hardhat`
+
+**NOTE:** create a `.env` file and add the private-key and rpc api-key in this file. Please add `.env` file to `.gitignore` as well.
+
+we will use above keys in hardhat.config.js file. 
+
+`npm i dotenv`
+
+If using openzeppelin then `npm install @openzeppelin/contracts` command to add the packages.
+
+**Compile Project**
+
+`npx hardhat compile`
+
+**Test Project**
+
+`npx hardhat test`
+
+**Deploy Project**
+
+`npx hardhat run scripts/deploy.js --network <network_name from hardhat.config.js file>`
+for eg: `npx hardhat run scripts/deploy.js --network polygon_test`
+
+**Reference:** Hardhat [docs]("https://hardhat.org/tutorial/setting-up-the-environment.html")

contracts/nft.sol

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+//SPDX-License-Identifier: Unlicense
+pragma solidity ^0.8.4;
+
+//import "hardhat/console.sol";
+import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
+import "@openzeppelin/contracts/utils/Counters.sol";
+import "@openzeppelin/contracts/access/Ownable.sol";
+
+/**
+  @title Creating Nfts
+  @dev Contract for creating nfts using ERC721. Unlike ERC20, ERC721 lacks a decimals field,
+       since each token is distinct and cannot be partitioned
+*/
+contract Nfts is ERC721URIStorage, Ownable {
+
+  using Counters for Counters.Counter;
+  Counters.Counter private _tokenIds;
+  using Strings for uint256;
+
+  mapping (uint256 => string) private _tokenURIs;
+
+  constructor() ERC721("SuperNFT", "SNFT") {}
+
+  /**
+    @dev miniting NFT
+   */
+  function mint(address recepient, string memory _tokenURI) public returns (uint) {
+
+    _tokenIds.increment();
+    uint256 newItemId = _tokenIds.current();
+    _mint(recepient, newItemId);
+    _setTokenURI(newItemId, _tokenURI);
+
+    return newItemId;
+  }
+
+}

hardhat.config.js

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+require("@nomiclabs/hardhat-waffle");
+// for using .env file which contains private info. 
+require('dotenv').config();
+const POLYGON_TEST_PRIVATE_KEY = process.env.POLYGON_TEST_PRIVATE_KEY;
+const POLYGON_TEST_API_KEY = process.env.POLYGON_TEST_API_KEY;
+
+// This is a sample Hardhat task. To learn how to create your own go to
+// https://hardhat.org/guides/create-task.html
+task("accounts", "Prints the list of accounts", async (taskArgs, hre) => {
+  const accounts = await hre.ethers.getSigners();
+
+  for (const account of accounts) {
+    console.log(account.address);
+  }
+});
+
+// You need to export an object to set up your config
+// Go to https://hardhat.org/config/ to learn more
+
+/**
+ * @type import('hardhat/config').HardhatUserConfig
+ */
+module.exports = {
+  // You can customize which network is used by default when running Hardhat by setting
+  // the config's defaultNetwork field. If you omit this config, its default value is "hardhat"
+  defaultNetwork: "polygon_test",
+  networks: {
+    hardhat: {
+    },
+    // rinkeby: {
+    //   url: "https://eth-mainnet.alchemyapi.io/v2/123abc123abc123abc123abc123abcde",
+    //   accounts: [privateKey1, privateKey2, ...]
+    // }
+    polygon_test: {
+      url: `https://rpc-mumbai.maticvigil.com/v1/${POLYGON_TEST_API_KEY}`,
+      chainId: 80001,
+      // The address to use as default sender. If not present the first account of the node is used
+      //from: ,
+      // Its value should be "auto" or a number. If a number is used, it will be the gas limit used by default in every transaction.
+      // If "auto" is used, the gas limit will be automatically estimated. Default value: "auto"
+      gas: "auto",
+      // Its value should be "auto" or a number. This parameter behaves like gas. Default value: "auto"
+      gasPrice: "auto",
+      // A number used to multiply the results of gas estimation to give it some slack due to the uncertainty 
+      // of the estimation process. Default value: 1
+      //gasMultiplier: 1,
+      // This field controls which accounts Hardhat uses. It can use the node's accounts (by setting it to "remote"), a list
+      // of local accounts (by setting it to an array of hex-encoded private keys), or use an HD Wallet. Default value: "remote"
+      accounts: [`0x${POLYGON_TEST_PRIVATE_KEY}`],
+      // You can use this field to set extra HTTP Headers to be used when making JSON-RPC requests. It accepts a JavaScript
+      // object which maps header names to their values. Default value: undefined
+      //httpHeaders: '',
+      timeout: 20000
+    }
+  },
+  solidity: {
+    version: "0.8.4",
+    settings: {
+      optimizer: {
+        enabled: true,
+        runs: 200
+      }
+    }
+  },
+  paths: {
+    sources: "./contracts",
+    tests: "./test",
+    cache: "./cache",
+    artifacts: "./artifacts"
+  },
+  mocha: {
+    timeout: 20000
+  }
+};