parsec_user_guide.md: slight usability tweaks

[anders94]

• npm -y init is not necessary, especially as npm install lines don't include --save
• npx hardhat with nothing specified is being deprecated in favor of npx hardhat init
• added scripts/ to make it more clear where hardhat.config.js is to be copied from

[HalosGhost]

utACK.

I appreciate the clean-up and simplifications! I won't have a chance to give a tACK till early next week, but I suspect that will be quick and simple.

[maurermi]

T-ACK. Appreciate the clean-up!