docs: remove unnecessary $ that begins each line of code for copy/paste (#19768)

Removing $ allows users to easily copy/paste the code blocks, otherwise they have to remove $ on each line of the paste.


----

### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [ ] Did you use `cdk-integ` to deploy the infrastructure and generate the snapshot (i.e. `cdk-integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: stevebanik

README.md

@@ -79,17 +79,17 @@ For a detailed walkthrough, see the [tutorial](https://docs.aws.amazon.com/cdk/l
 Install or update the [AWS CDK CLI] from npm (requires [Node.js ≥ 14.15.0](https://nodejs.org/download/release/latest-v14.x/)). We recommend using a version in [Active LTS](https://nodejs.org/en/about/releases/)
 
 ```console
-$ npm i -g aws-cdk
+npm i -g aws-cdk
 ```
 
 (See [Manual Installation](./MANUAL_INSTALLATION.md) for installing the CDK from a signed .zip file).
 
 Initialize a project:
 
 ```console
-$ mkdir hello-cdk
-$ cd hello-cdk
-$ cdk init sample-app --language=typescript
+mkdir hello-cdk
+cd hello-cdk
+cdk init sample-app --language=typescript
 ```
 
 This creates a sample project looking like this:
@@ -113,7 +113,7 @@ export class HelloCdkStack extends cdk.Stack {
 Deploy this to your account:
 
 ```console
-$ cdk deploy
+cdk deploy
 ```
 
 Use the `cdk` command-line toolkit to interact with your project: