Nitpicks for sections 2-6

[ianjmacintosh]

I just finished up the React Hooks workshop and did some nitpicking along the way. Here's some more typo fixes! 🔍

• 7e57e9a94aacf243322390bca068d25fabaf3f9f: Write React with an uppercase R
• 0cc2ac6bf72ea947f09584fdbf79d9aa077936cf: Remove extra "o" in synchronized
• 2c9950a965040f5ba22ddf7f78ffbe0959767f4d: Capitalize a first letter of a sentence
• fadae75529f0ee208c5bdb6c8c110028a8946b18: Move loose clause off to its own sentence