Add readme for internal

include/ccmath/internal/README.md

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+# CCMath Internal Headers Info
+> [!CAUTION]
+> This directory contains internal headers for the CCMath library. These headers are not intended for public use and are subject to change at any time. They are used for internal implementation details and are not guaranteed to be stable or to have a stable API. Assume anything included here directly could change its signature at any moment.
+
+## Folders
+- `config`: Predefined macros and configuration settings for the library.
+- `helpers`: Helper functions and classes used for internal implementation details.
+- `predef`: Predefined macro wrappers for compiler and platform-specific features.
+- `support`: Support classes and functions for internal implementation details.
+- `types`: Custom type definitions and wrappers for cmath types.