docs: update jest section

README.md

@@ -318,24 +318,26 @@ npm install -D jest ts-jest
 `jest` is the testing framework itself, and `ts-jest` is just a simple function to make running TypeScript tests a little easier.
 
 ### Configure Jest
-Jest's configuration lives in `package.json`, so let's open it up and add the following code:
-```json
-"jest": {
-    "globals": {
-      "__TS_CONFIG__": "tsconfig.json"
-    },
-    "moduleFileExtensions": [
-      "ts",
-      "js"
-    ],
-    "transform": {
-      "^.+\\.(ts)$": "./node_modules/ts-jest/preprocessor.js"
-    },
-    "testMatch": [
-      "**/test/**/*.test.(ts|js)"
-    ],
-    "testEnvironment": "node"
-  },
+Jest's configuration lives in `jest.config.js`, so let's open it up and add the following code:
+```js
+module.exports = {
+	globals: {
+		'ts-jest': {
+			tsConfigFile: 'tsconfig.json'
+		}
+	},
+	moduleFileExtensions: [
+		'ts',
+		'js'
+	],
+	transform: {
+		'^.+\\.(ts|tsx)$': './node_modules/ts-jest/preprocessor.js'
+	},
+	testMatch: [
+		'**/test/**/*.test.(ts|js)'
+	],
+	testEnvironment: 'node'
+};
 ```
 Basically we are telling Jest that we want it to consume all files that match the pattern `"**/test/**/*.test.(ts|js)"` (all `.test.ts`/`.test.js` files in the `test` folder), but we want to preprocess the `.ts` files first. 
 This preprocess step is very flexible, but in our case, we just want to compile our TypeScript to JavaScript using our `tsconfig.json`.