Update React Scripts and Remove Jest from devDependency

Fix Jest conflict from React Scripts - Jest was manually added
originally  due to this [issue](testing-library/react-testing-library#662).
Latest update of React Scripts has a mroe recent update of Jest
and we can safely move away from manually configuring Jest on
our own.

.env.example

@@ -1 +0,0 @@
-SKIP_PREFLIGHT_CHECK=true

README.md

@@ -6,12 +6,10 @@ Install dependencies:
 npm i
 ```
 
-IMPORTANT: Create a `.env` file and copy the keys and values from `.env.example`.
-
 Running the client server locally:
 
 ```bash
-npm run start:client
+npm run start
 ```
 
 Running tests:
@@ -20,7 +18,7 @@ Running tests:
 npm run test
 ```
 
-Note: Even if you aren't developing the backend, you should set up the the [backend](https://github.com/codebuddies/backend) and run it locally so that the frontend has a local API to talk to. 
+Note: Even if you aren't developing the backend, you should set up the the [backend](https://github.com/codebuddies/backend) and run it locally so that the frontend has a local API to talk to.
 
 ## **Overview of Codebuddies**