Docs: Clarify Node version in dev environment setup instructions

[dreamorosi]

What were you searching in the docs?

Under the "Setup" section of the Contributing guidelines there are some prerequisites and instructions to setup the development environment.

A first-time contributor tried to follow the instructions but missed that Node.js 16 is the default version.

Is this related to an existing documentation section?

https://github.com/awslabs/aws-lambda-powertools-typescript/blob/main/CONTRIBUTING.md#setup

How can we improve?

The list of items with versions is immediately above some shell commands, readers might focus on these and miss the above. 

We could make the info pop a bit more using a note.

Got a suggestion in mind?

Something along the lines of:

Note
In order for the commands below to work you need Node.js 16.x and npm 8.x

Acknowledgment

• I understand the final update might be different from my proposed suggestion, or refused.

[github-actions]

⚠️ COMMENT VISIBILITY WARNING ⚠️

Comments on closed issues are hard for our team to see.
If you need more assistance, please either tag a team member or open a new issue that references this one.
If you wish to keep having a conversation with other community members under this issue feel free to do so.