feat(tools): Add a link to the Helix editor

[usagi-flow]

Fixes #1696

[Manishearth]

cc @pietroalbini thoughts?

in general the intent of this has kinda been to be well known editors but perhaps this section needs to be restructured, there are a LOT more editors with rust support than there were at the time of this page's writing. Unsure what we should be doing here.

Also the intent of this has not been to advertise editors, but rather to get people links to how they can make $language work with their editor. As such I'm not sure if we need to mention editors with builtin support (or perhaps we should mention it in a different way?)

[usagi-flow]

Thank you for your quick feedback!

Maybe it could be worth considering an approach like editorconfig.org, which differentiates between editors with native support and editors which require a plugin. However, both groups of editors are shown.

I think that approach would have two advantages:

• Both new and advanced Rust developers would have a central overview on a site where (IMHO) they would expect it.
• Not including editors with native support could leave the website visitor wondering if - or even worse, assuming that - an editor they know doesn't support Rust (well enough?), because it isn't listed.

To summarize, I believe the question boils down to what kind of information we want to present to the visitor:

• An overview of supported editors.
• A very basic guide on how to get Rust support in editors without native support.

[Rudxain]

@usagi-flow

This implements #1696.

I recommend using closes "GH syntax"

[senekor]

Hi @usagi-flow, I would like to merge this.

• There is a free spot in the 2x4 grid, adding helix will make it look nice.
• According to the most recent Rust survey, helix is actually quite popular among Rust devs (8.9%).
• It's true that the purpose of the whole List is becoming more questionable as Rust is quite mature and established at this point. But I think that question can / should be resolved separately.

The order seems a little random to me at the moment, but I might sort them all according to popularity in a different PR.

I know it's been a while. Would you like to get it over the finish line or do you want me to take over?

[usagi-flow]

Thank you @senekor for taking this PR into consideration! If that's OK, I'll have a look at it tomorrow and rebase the branch accordingly.

[usagi-flow]

@senekor Sorry for letting you wait, but here's the rebased branch with the adjusted link!

[senekor]

Thank you!