Update sample code in README

[josh11b]

Description of the bug:

The examples in the README need to be updated to reflect the change to package syntax from proposal https://github.com/carbon-language/carbon-lang/pull/3927 .

Link to documentation:

https://github.com/carbon-language/carbon-lang/blob/trunk/README.md

What should it say instead?

package <something> api; should just be package <something>;

Any other information, logs, or outputs that you want to share?

No response

[ryoari]

Hi @josh11b, I'm interested in this issue and have started working on updating the README to reflect the changes from proposal #3927. I'll make sure to update all relevant examples and submit a pull request soon.