Add spaces in add_theme_support docs code

[kapilpaul]

Description

Added missing space in theme support docs

Types of changes

Updated the documentation

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[github-actions]

👋 Thanks for your first Pull Request and for helping build the future of Gutenberg and WordPress, @kapilpaul! In case you missed it, we'd love to have you join us in our Slack community, where we hold regularly weekly meetings open to anyone to coordinate with each other.

If you want to learn more about WordPress development in general, check out the Core Handbook full of helpful information.

[talldan]

Thanks for this, congrats on your first contribution!

edit: I've just updated the PR title—these appear in changelogs for Gutenberg, just in case you're wondering why.