Initial implementation of the ESLint config and ignore pattern

The `.eslintrc.js` configuration file has been placed in the project
root next to the `.eslintignore` file that defines the ignore pattern.
It specifies the environments (1) which define global variables that
are predefined:

- `browser` - browser global variables.
- `node` - Node.js global variables and Node.js scoping.

References:

  (1) https://eslint.org/docs/user-guide/configuring#specifying-environments

GH-15

.eslintignore

@@ -0,0 +1,13 @@
+# Copyright (C) 2018-present Arctic Ice Studio <[email protected]>
+# Copyright (C) 2018-present Sven Greb <[email protected]>
+#
+# Project:    Nord Docs
+# Repository: https://github.com/arcticicestudio/nord-docs
+# License:    MIT
+
+.cache/*
+build/*
+content/*
+**/node_modules/*
+public/*
+static/*

.eslintrc.js

@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2018-present Arctic Ice Studio <[email protected]>
+ * Copyright (C) 2018-present Sven Greb <[email protected]>
+ *
+ * Project:    Nord Docs
+ * Repository: https://github.com/arcticicestudio/nord-docs
+ * License:    MIT
+ */
+
+/**
+ * @file The ESLint configuration.
+ * @author Arctic Ice Studio <[email protected]>
+ * @author Sven Greb <[email protected]>
+ * @see https://github.com/babel/eslint-plugin-babel#rules
+ * @see https://github.com/tc39/proposal-optional-chaining
+ */
+
+module.exports = {
+  env: {
+    browser: true,
+    node: true
+  }
+};