Simplify build steps example

[PatKamin]

Description

Less steps in a build example in README:

• do not mix usage of make and cmake, cmake handles all that is needed
• cmake handles build dir creation

Preview: https://github.com/PatKamin/unified-memory-framework/tree/simplify-build-steps?tab=readme-ov-file#linux

Checklist

• Code compiles without errors locally
• All tests pass locally
• CI workflows execute properly

• CI workflows, not executed per PR (e.g. Nightly), execute properly
• New tests added, especially if they will fail without my changes
• Added/extended example(s) to cover this functionality
• Extended the README/documentation
• All newly added source files have a license
• All newly added source files are referenced in CMake files
• Logger (with debug/info/... messages) is used