Two typos in demo.typ

[raenye]

polylux/examples/demo.typ

Lines 34 to 44 in 19eb47e

	#slide(title: "A title")[
	Let's explore what we have here.
	On the top of this slide, you can see the slide title.
	We used the `title` argument of the `#slide` function for that:
	```typ
	#slide(title: "First slide")[
	...
	]
	```

"A title" ≠ "First slide"

polylux/examples/demo.typ

Line 218 in 19eb47e

`start` can also be omitted, then it starts with the first subside:

s/subside/subslide/