docs: document debug CMake builds

[kiwigitops]

Motivation

README source-build instructions document the default CMake flow, but they do not show how to build MIGraphX in debug mode even though the project defaults CMAKE_BUILD_TYPE to Release. This addresses the missing debug-build guidance requested in #958.

Technical Details

• Document -DCMAKE_BUILD_TYPE=Debug in the CMake build section.
• Mention RelWithDebInfo for optimized builds that still include debug symbols.

Why this adds value: developers can now configure debug or debug-symbol builds without reading CMakeLists.txt or guessing the supported CMake build types.

Validation performed:

• git diff --check

Documentation updated:

• README.md

Checks not run:

• Full MIGraphX build and docs build, because this environment does not have the ROCm build dependencies required by the project.

Changelog Category

Add a CHANGELOG.md entry for any option other than Not Applicable

• • Added: New functionality.
• • Changed: Changes to existing functionality.
• • Removed: Functionality or support that has been removed. (Compared to a previous release)
• • Optimized: Component performance that has been optimized or improved.
• • Resolved Issues: Known issues from a previous version that have been resolved.
• • Not Applicable: This PR is not to be included in the changelog.

Closes #958