Docs Minor Change: Fuelup Installation Guide

[Tlazypanda]

Expected Behavior

Currently the docs link - Fuelup check toolchain on running the fuelup show command gives output which mentions beta-4-x86_64-unknown-linux-gnu (default) as the active toolchain.

But the last line in the docs mention - As you can see, the beta-5 toolchain is active 🚀. This might be confusing to devs looking to setup fuel.

Actual Behavior

Replace the actual output with the right output (beta-5)