Add cargo generate template for start project

[HKalbasi]

I create a template via cargo generate for bootstrap new projects.

Currently it supports arduino-uno and arduino-leonardo (leonardo is untested, I just have one uno at home) but adding boards is very easy.

I think it is useful for beginners as well as professionals. But there is valid reasons for rejecting this PR (like cargo generate is slow to install)

[Rahix]

Funnily enough just yesterday I randomly got to chat with one of the cargo-generate maintainers about using it for projects in the embedded space, like avr-hal.

So yes, a template is very much a thing we want, to lower the entry barrier and to prevent the load of issues we get from people accidentally skipping steps in the instructions. There is also an issue about it already: #54 :) The plan is to track the template in a separate branch of this repository for now.

As we're currently doing a big refactor/rewrite of avr-hal (see #130), I think we should wait with providing the template until that's completed. So I'd leave this PR open until we're done and then pull in your work as a basis, if that's okay with you :)

[HKalbasi]

:)) I did it simply because no one had done it before. (I was not aware of #54) I saw this project today (Searching "how I can program my arduino using rust") and found it unnecessarily hard to start with (relative to arduino ide and C) so I tried to make a step forward.

There PR is just for replacing initial steps in Readme.md and template is in this repo. It already works and it should be easy to update it when that great upgrade become ready. But if you see benefit in delaying it until then, that is ok.

I don't think track the template in a branch is a good idea. Specially if cargo-generate clone whole repo it will be slow to download. Keeping template in the tree make sense because of syncing template with code but cargo-generate can't handle this AFAIK. But if you decide to do this or making a separate repository, feel free to use my code and tell me to deprecate my template in favor of yours.

[HKalbasi]

Seems it is fixed in next branch. Thanks for great work!