Add smallpt licence to example

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

When the smallpt example was added to this repo, it was added without its licence, which clearly states that where it is included, it should contain the copyright notice and this permission notice. The original licence for this software was found here https://github.com/wedusk101/smallpt/blob/master/LICENSE.txt

Fixes # (issue)

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.78%. Comparing base (98585e8) to head (e74181a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #304   +/-   ##
=======================================
  Coverage   81.78%   81.78%           
=======================================
  Files          20       20           
  Lines         950      950           
  Branches       87       87           
=======================================
  Hits          777      777           
  Misses        173      173           

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[anutosh491]

Hey @mcbarton, its just a bunch of comments and I know our deployment fails for now running smallpt. But we could take this in, if you could confirm things working with a local build. Let us know if that works !