Update index.md

stuck in #6

Let’s change the theme to minima :

  1. At the top of this Pull Request, click the Files changed tab.
  2. Click the icon to enter edit mode and change the theme: to minima .
  3. Scroll to the bottom of the window to create a commit.
  4. Enter a commit message then click Commit changes .

Don’t worry, if you don’t like this theme you can always change it later.

that’s the mission but i cannot understand the second line.
i entered edit mode yes but what does the change the theme: to minima mean?