Fix a few cosmetic issues in the primary README

[abeltrano]

Type

• Bug fix
• Feature addition
• Feature update
• Documentation
• Build Infrastructure

Side Effects

• Breaking change
• Non-functional change

Goals

• Ensure the README doesn't have formatting errors.

Technical Details

• Remove an extraneous backtick.
• Move a [!WARNING] block to be un-indented due to a recent change described here that introduced a regression for tabbed support.

Test Results

• Visually inspected new rendered README and confirmed no formatting issues are present.

Reviewer Focus

• Consider whether there are any formatting, spelling, or grammar errors that need fixing.

Future Work

• None

Checklist

• Build target all compiles cleanly.
• clang-format and clang-tidy deltas produced no new output.
• Newly added functions include doxygen-style comment block.