Update readme for env var syntax

[Jdubrick]

Description

• Adds a note to the readme to make users aware of certain syntax required for Lightspeed Core environment variables

Which issue(s) does this PR fix or relate to

N/A

PR acceptance criteria

• Tests updated and passing
• Documentation updated
• Built-in TechDocs updated if needed. Note that TechDocs changes may need to be reviewed by a Product Manager and/or Architect to ensure content accuracy, clarity, and alignment with user needs.

How to test changes / Special notes to the reviewer

[Jdubrick]

fyi @benwilcock