Note possible BOM in payload

[idorurez]

Suggestions:

1. Print deserialization error if any
2. Add warning/note about possible BOM in the hosted .json.

I was hitting "InvalidInput" but couldn't figure it out until I read: https://arduinojson.org/v6/api/misc/deserializationerror/

.. and found out I had a few extra bytes:

         00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F

00000000   EF BB BF 7B 0A 20 20 20 20 22 74 79 70 65 22 3A  {.    "type":
00000010   20 22 65 73 70 33 32 2D 66 6F 74 61 2D 6D 61 69   "esp32-fota-mai
00000020   6E 2D 77 65 61 74 68 65 72 22 2C 0A 20 20 20 20  n-weather",.
00000030   22 76 65 72 73 69 6F 6E 22 3A 20 32 2C 0A 20 20  "version": 2,.

I then used Notepad++ to fix it: Encoding >> Encode in UTF-8 without BOM