COALESCE could use some better examples

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/15/functions-conditional.html
Description:

Regarding:
https://www.postgresql.org/docs/current/functions-conditional.html

I ran into a situation where COALESCE was used like this

```
SELECT * FROM table WHERE COALESCE(col_1, col_2, col_3) >= 5
```

and didn't understand how it worked, and the examples don't really help
because they only use COALESCE like

```
SELECT COALESCE(..)
```

I asked and answered a question on stackoverflow with a pretty good example
of this, you could consider adding to your page.

Thank you :))

Stackoverflow question link:
https://stackoverflow.com/questions/74057319/coalesce-in-postgresql-conditional-displaying-seemingly-undocumented-behavior