Add .eslintrc to RN project template (#23901)

Summary:
The goal of this PR is to enable eslint checks in the projects generated by `react-native init` command. I added `template/_eslintrc` file, that would be replaced in an initialized project with `.eslintrc` file. This PR comes in parallel with https://github.com/react-native-community/react-native-cli/pull/229

[General] [Added] - Added `.eslintrc` file to generated template.
Pull Request resolved: https://github.com/facebook/react-native/pull/23901

Differential Revision: D14561084

Pulled By: cpojer

fbshipit-source-id: 6eb717bf03c45d83ae8a393e6a0abb79e1e2f915

packages/eslint-config-react-native-community/index.js

@@ -30,6 +30,14 @@ module.exports = {
     },
   },
 
+  overrides: {
+    files: ['**/__tests__/**/*.js', '**/?(*.)(spec|test).js'],
+    env: {
+      jest: true,
+      'jest/globals': true,
+    },
+  },
+
   // Map from global var to bool specifying if it can be redefined
   globals: {
     __DEV__: true,

packages/eslint-config-react-native-community/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@react-native-community/eslint-config",
-  "version": "0.0.2",
+  "version": "0.0.3",
   "description": "ESLint config for React Native",
   "main": "index.js",
   "repository": {

template/_eslintrc.js

@@ -0,0 +1,4 @@
+module.exports = {
+  root: true,
+  extends: '@react-native-community',
+};