Fix hyperlinks in the FAQ notebook

[eendebakpt]

The hyperlinks in the contents section of the FAQ did not work properly. In this PR we update the hyperlinks. The formatting is a bit error prone (changing the title means you have to manually update the contents table), but I could not find a method to auto-generate the contents from within the notebook.

Python script to update the links

Updating the links can be done by replacing the headers with this script

import re

t="""
- [What is GST?](#what_is_gst)
- [What is pyGSTi?](#what_is_pygsti)
"""

for idx,ln in enumerate(t.split('\n')):
    section_title=re.findall('\[.*?\]', ln)
    if len(section_title)!=1:
        continue
    
    hyperlink='(#' + section_title[0][1:-1].replace(' ', '-') +')' 
    #print(f'{idx}: {s}')
    m=re.sub('\]\(.*\)',']'+ hyperlink, ln)
    print(m)

@coreyostrove