Change your text file name to "doc.txt" and put it in this directory /Users/***/.vscode/extensions/thinkingthigh.dnuorassem-1.0.3/docs/ (macOS) C:\Users\***\.vscode\extensions\thinkingthigh.dnuorassem-1.0.3\docs\ (Windows)
Press command+shift+, (macOS) or ctrl+shift+, (Windows) to launch it.
Function buttons("↑","↓","goto"...) are displayed on the status bar.