Use Mermaid to create flowchart that shows how to add software to EESSI

[xinan1911]

No description provided.

[laraPPr]

@Xin I think you'll also need to update the requirements because this is what it looked like when I tested it

[laraPPr]

you'll have to add this to mkdocs.yml

extra_javascript:
  - https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs

and use this:

<pre class="mermaid">
</pre>

instead of:

'''mermaid
'''

[xinan1911]

@laraPPr Doen. Could you take a look again?

[laraPPr]

The graphs are now rendering correctly. I have a few more suggestions to make the page look a little better and to use the hyperlink feature of Mermaid. But @xinan1911 I'm willing to merge it if you do not think the changes are necessary.