Create a New Repo perun-rs for the perun lab

[choeppler]

The perun team has been working on a rust implementation of the go-perun library for embedded devices, which we'd like to add to the labs project. Could you please create a perun-rs repo and add add this to the labs project? Thank you!

• GitHub repo to add: https://github.com/hyperledger-labs/perun-rs
• Associated lab proposal: original lab proposal
• Lab to be added to: perun

[ryjones]

here you go!