Update README-main-functions.md

[anakin004]

Summary of Changes:

Formatted a set of best practices and guidelines related to using SDL (Simple DirectMedia Layer) for managing entry points, callbacks, platform-specific considerations, and when to include or skip SDL_main.h.

Description:

The changes involve outlining several SDL-specific best practices, which include:

• Always including SDL_main.h in one source file to prevent conflicts.
• Avoiding redefinition of the main function when using SDL’s entry point system.
• Using SDL’s callback system for more complex applications that require event handling and control over the app’s flow.
• Platform-specific considerations, such as SDL handling platform-specific entry points on Windows.
• Guidance on when to omit SDL_main.h, such as when integrating SDL into an existing application or scripting environment.

These practices are intended to ensure the stability and compatibility of SDL applications across different platforms and setups.

Existing Issue(s):

This change does not fix an open issue but provides guidance on SDL best practices for future development.