Update User Guide with deploying to GitHub User pages (#3510)

Author: aaronlna

packages/react-scripts/template/README.md

@@ -2012,12 +2012,18 @@ For more information see [Add Firebase to your JavaScript Project](https://fireb
 **The step below is important!**<br>
 **If you skip it, your app will not deploy correctly.**
 
-Open your `package.json` and add a `homepage` field:
+Open your `package.json` and add a `homepage` field for your project:
 
-```js
+```json
   "homepage": "https://myusername.github.io/my-app",
 ```
 
+or for a GitHub user page:
+
+```json
+  "homepage": "https://myusername.github.io",
+```
+
 Create React App uses the `homepage` field to determine the root URL in the built HTML file.
 
 #### Step 2: Install `gh-pages` and add `deploy` to `scripts` in `package.json`
@@ -2048,6 +2054,18 @@ Add the following scripts in your `package.json`:
 
 The `predeploy` script will run automatically before `deploy` is run.
 
+If you are deploying to a GitHub user page instead of a project page you'll need to make two
+additional modifications:
+
+1. First, change your repository's source branch to be any branch other than **master**.
+1. Additionally, tweak your `package.json` scripts to push deployments to **master**:
+```diff
+  "scripts": {
+    "predeploy": "npm run build",
+-   "deploy": "gh-pages -d build",
++   "deploy": "gh-pages -b master -d build",
+```
+
 #### Step 3: Deploy the site by running `npm run deploy`
 
 Then run: