add rust version check and install link to readme

[ccbaumler]

fixes #32

I was cleaning up my account a few days back and deleted cargo without thinking about it. I got this error and realized my mistake. After reinstalling rust everything is running again!
I think you may want to add the link to install rust in your install instructions!

$ pip install sourmash_plugin_directsketch==0.3.0

Collecting sourmash_plugin_directsketch==0.3.0
  Using cached sourmash_plugin_directsketch-0.3.0.tar.gz (152 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Preparing metadata (pyproject.toml) ... error
  error: subprocess-exited-with-error

  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [8 lines of output]
      error: rustup could not choose a version of cargo to run, because one wasn't specified explicitly, and no default is configured.
      help: run 'rustup default stable' to download the latest stable release of Rust and set it as your default toolchain.

      Cargo, the Rust package manager, is not installed or is not on PATH.
      This package requires Rust and Cargo to compile extensions. Install it through
      the system's package manager or via https://rustup.rs/

      Checking for Rust toolchain....
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.

[bluegenes]

Thanks for the PR! Thinking on it -- I'd like to avoid having folks install rust directly. But that means I should actually describe the install process from conda using environment.yml file in the README.

I'm not sure how this interacts with existing cargo on your system - would assume if you already had rust it would not reinstall via conda. Which is maybe why deleting cargo borked everything?

Let's keep this open for now and I'll do some testing!

[bluegenes]

or better yet, I should go ahead and make this conda installable

[ccbaumler]

That sounds like a much nicer solution!

[bluegenes]

@ccbaumler can I close this? Aka, did the conda installation solve this for you?

[ccbaumler]

Sounds good to me. I believe that my issue has been solved.