Add recipe for completing-read-sly

[enzuru]

Brief summary of what the package does

This package lets you search through Common Lisp symbols defined in SLY using Emacs' built-in competing-read function.

Direct link to the package repository

https://github.com/enzuru/completing-read-sly

Your association with the package

I am the original author and current maintainer.

Relevant communications with the upstream package maintainer

*None needed

Checklist

• The package is released under a GPL-Compatible Free Software License
• I've read CONTRIBUTING.org
• I've used the latest version of package-lint to check for packaging issues, and addressed its feedback
• My elisp byte-compiles cleanly
• I've used M-x checkdoc to check the package's documentation strings
• I've built and installed the package using the instructions in CONTRIBUTING.org

[riscy]

I think per #8850 we're still waiting to hear back from the SLY repo re: upstreaming this.

On a quick glance, the checklist and the code look good and I can see the use. But upstreaming this is my hoped-for resolution, because in general tiny bits of code like this could be written around ANY package out there, and you could imagine how bulky the MELPA index could become if we merged everything like this without inhibition.

[riscy]

I'm not too familiar with this family of packages, but you may also want to consider upstreaming to another relevant package already in the MELPA index. On a quick search https://melpa.org/#/glue comes up in this space (but it may or may not be an appropriate choice).

[enzuru]

@riscy will go ahead and either submit this to documentation or write a blog post -- thank you