chore: update env file

We're currently seeing the following error for the gdk evaluate command:

cp: evaluation_scripts/code_suggestions/.env.example: No such file or directory
make[1]: *** [/Users/gosiaksionek/gitlab-development-kit/gitlab-eli5/evaluation_scripts/code_suggestions/.env] Error 1
make: *** [gitlab-eli5-update-timed] Error 2

This is due to how we have opted to approach our ENV variables. The solution takes place in two MRs:

• MR1: This MR for our documentation.
• MR2: A follow-up to Support running ELI5 service (gitlab-org/gitlab-development-kit!3747 - merged) • David O'Regan, Ash McKenzie • 17.2 to update the Make file.
  • Add support for code suggestions in gdk (simila... (#14 - closed) • Unassigned