How to add empty spaces into MD markdown readme on GitHub?

You can use <pre> to display all spaces & blanks you have typed. E.g.:

<pre>
hello, this is
   just an     example
....
</pre>

Instead of using HTML entities like   and   (as others have suggested), you can use the Unicode em space (8195 in UTF-8) directly. Try copy-pasting the following into your README.md. The spaces at the start of the lines are em spaces.

The action of every agent <br />
  into the world <br />
starts <br />
  from their physical selves. <br />

Markdown really changes everything to html and html collapses spaces so you really can't do anything about it. You have to use the   for it. A funny example here that I'm writing in markdown and I'll use couple of         here.

Above there are some   without backticks