docs: replace curl link

[calldelegation]

curl -sSf https://install.fuel.network/fuelup-init.sh | sh"

--proto '=https' --tlsv1.2 can be removed right away as suggested by @cold-briu

[cold-briu]

Just FYI: this idea comes from a discussion in slack. The final goal is something like this:

Now:
curl --proto '=https' --tlsv1.2 -sSf \ https://install.fuel.network/fuelup-init.sh | sh

Ideal:
curl -sSf https://fuel.network/install | sh

The new url might require changes on the main host.

CC @JoshuaBatty