Keep concrete syntax examples and simplify fork instructions

Author: aurorascharff

CONTRIBUTING.md

@@ -46,6 +46,33 @@ In particular, you should prefer named `function` declarations over `const myFun
 
 #### Don't use features that aren't standardized yet.
 
+For example, **don't** write this:
+
+```js
+function Greeting({isLoggedIn}) {
+  return do {
+    if (isLoggedIn) {
+      <h1>Welcome back!</h1>;
+    } else {
+      <h1>Please sign in.</h1>;
+    }
+  };
+}
+```
+
+The [`do` expression syntax](https://github.com/tc39/proposal-do-expressions) is still experimental.
+
+Instead, **do** write this:
+
+```js
+function Greeting({isLoggedIn}) {
+  if (isLoggedIn) {
+    return <h1>Welcome back!</h1>;
+  }
+  return <h1>Please sign in.</h1>;
+}
+```
+
 Ignore this rule if you're specifically describing an experimental proposal. Make sure to mention its experimental nature in the code and in the surrounding text.
 
 ### Style

README.md

@@ -15,7 +15,7 @@ This repo contains the source code and documentation powering [react.dev](https:
 ### Installation
 
 1. `cd react.dev` to go into the project root
-2. `git remote add my-fork-name https://github.com/YOUR_USERNAME/react.dev.git` to add your fork as a remote (replace `YOUR_USERNAME` with your GitHub username; only needed once)
+2. `git remote add my-fork-name https://github.com/YOUR_USERNAME/react.dev.git` to add your fork as a remote. Replace `YOUR_USERNAME` with your GitHub username. You only need to do this once.
 3. `yarn` to install the website's npm dependencies
 
 ### Running locally