[Docs] create setup.md

Root file for the docs directory to help newbies find info on setting up the plugin.

Author: tiefling

docs/setup.md

@@ -0,0 +1,43 @@
+In order to use the react eslint plugin do the following...
+
+1. At the root of your project type <code>npm install --save-dev eslint-plugin-react</code>
+2. Check your package.json 'devDependencies' for the following entries (version numbers may vary, but it's important that **the eslint version matches the peerDependency version in eslint-plugin-react**)...
+<pre>
+  "devDependencies": {
+    "eslint": "^7.3.1",
+    "eslint-plugin-react": "^7.10.3"
+  }
+</pre>
+3. If configuring using package.json add the following under 'eslintConfig'...
+<pre>
+  "eslintConfig": {
+    "plugins": [
+      "react"
+    ]
+   }
+</pre>
+Else, in your eslint configuration file (.eslintrc) add the following...
+<pre>
+  {
+    "plugins": [
+      "react"
+    ]
+  }
+</pre>
+4. Configure the rules you want to use according to the [rules docs](/docs/rules). Here's a sample of some of mine...
+<pre>
+  "eslintConfig": {
+    "rules": {
+      "no-unused-vars": 2,
+      "react/jsx-uses-vars": 2,
+      "react/require-extensions": 0,
+      "react/jsx-sort-prop-types": 0,
+      "react/prop-types": [2, {
+        "ignore": ["children"],
+        "skipUndeclared": false
+      }]
+    }
+   }
+</pre>
+
+<i>You can read more about configuring ESLint plugins at http://eslint.org/docs/user-guide/configuring#configuring-plugins</i>