How to add ASCII art to a README
ASCII art only lines up when every space and line break is kept. A README that uses a proportional font will break the drawing.
Paste ASCII art into Markdown
Wrap the characters in a fenced code block. That forces a monospaced font and keeps the spaces that form the picture.
When a PNG is safer
If the page or chat app restyles text, download a PNG from the image converter or the ASCII-to-image tool and embed that instead.