Documentation: how to use feed URLs containing parameters

The following could be a nice completion for the documentation and presentation of the widget:
- Feed-URLs (links to the RSS-source) which contain parameters are not valid, as the parameters of the feed-URL are treated as parameters for the widget-URL and are thus effectively discarded.
- However, this does not happen if the feed-URL has been previously URL-encoded by replacing all characters like `?`. `&`, etc. by their respective percent-encoding.
- If the Feed-URL has not been previously encoded, the widget does not always return an error, showing instead "nothing new".

Since the Feed-URL I am using is semi-private, I cannot give a real example. But my use case is similar to the following:

The example Feed-URL is `https://website.domain/feed?user=123456789&content=all`

1. Without encoding:
- `[COMA_SEPARATED_SOURCES]=https://website.domain/feed?user=123456789&content=all`
- Widget-Link: `https://notion-widget-rss.vercel.app/?sources=https://website.domain/feed?user=123456789&content=all&sinceDays=14`
> This results in the widget showing "nothing new" and an empty feed.
2. With encoding:
- `[COMA_SEPARATED_SOURCES]=https%3A%2F%2Fwebsite.domain%2Ffeed%3Fuser%3D123456789%26content%3Dall`
- Widget-Link: `https://notion-widget-rss.vercel.app/?sources=https%3A%2F%2Fwebsite.domain%2Ffeed%3Fuser%3D123456789%26content%3Dall&sinceDays=14`
> This works as desired.


Thank you very much for the widget, it works very nicely and I am glad I found a way to track new uploads to my online courses without having to log-in every single time. :)