Enhance Tkinter Crypto Viewer UI and README

[gmolate]

This commit includes several improvements to the Tkinter desktop application:

• UI Aesthetics:

  • Applied the 'clam' ttk theme for a more modern base.
  • Implemented a light color scheme with improved visual hierarchy.
  • Standardized fonts to Helvetica with adjusted sizes for better readability.
  • Increased padding and spacing for a cleaner layout.
  • Set initial window geometry to 500x700 for a more balanced view.

• UI Responsiveness:

  • Modified API configuration buttons to stack vertically in narrow window layouts, improving usability in portrait-style orientations.
  • Ensured main content areas (like the balance tree) utilize fill and expand properties for better resizing behavior.

• README.md Update:

  • Rewrote content with a friendly and engaging Chilean Spanish tone.
  • Clarified existing features and instructions.
  • Strengthened the security advice section.