updated type system on readme

[siv2r]

Description

Addresses #97

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Documentation Update

Checklist:

• My code follows the style guidelines (Clean Code) of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests/screenshots (if any) that prove my fix is effective or that my feature works.
• I have tested my code with OPTION_BUILD_SANITIZER and OPTION_TEST_MEMORYCHECK.
• I have tested with Helgrind in case my code works with threading.

If you are unclear about any of the above checks, have a look at our documentation here

[viferga]

Can you add the future? #97 (comment)

[siv2r]

I added the definition for Future. Sorry for the delay :)