generate-release must be run from the generate-release folder

[BD103]

generate-release assumes that it is run from the generate-release folder, so it always writes to ../release-content. This is an issue when it is called from the root directory using cargo run -p generate-release, and tripped me up when I first started using the tool.

I propose that generate-release always switch into the correct directory, so it can keep these assumptions. If this were a shell script I'd do something like the following, but it may be more involved for Rust:

bevy-website/generate-errors/generate_errors.sh

Lines 3 to 4 in 45998c4

	# Switch to script's directory, letting it be called from any folder.
	cd $(dirname $0)

[alice-i-cecile]

This tripped me up too; we should fix this.