added utf-8 resonvling encoding issue in f.read

[AntonisCSt]

Hi,

thanks for the tutorial!
I propose adding this cause I had the following issue when running main (with python 3.10 and installing poetry):

  File "C:\Users\AX-St\DataTalksClub\Prometheus tutorial\pycon22-prometheus-workshop\app\main.py", line 15, in <module>
    html_string = f.read()
  File "C:\Users\AX-St\AppData\Local\Programs\Python\Python310\lib\encodings\cp1253.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x9f in position 1420: character maps to <undefined> 

what do you think?