docs(examples): made SAM CLI version requirement more explicit

[dreamorosi]

Description of your changes

Multiple users #1273 and #1281 reported having issues with the SAM examples in this repo due to the readme file not being explicit about the minimum version required for SAM CLI.

Node.js 18.x support was released in AWS SAM CLI version 1.65, users running a lower version and trying to compile the version run into the following error during compile:

Error: 'nodejs18.x' runtime is not supported

This PR adds a visual callout to the readme that specifies the version and links to instruction on how to upgrade.

How to verify this change

See the updated readme, which looks like the image below (red box added to highlight changes):

Related issues, RFCs

Issue number: #1273

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding changes to the examples
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published
• The PR title follows the conventional commit semantics

Breaking change checklist

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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