Unclear model for installing/using a plugin alongside LH

[paulirish]

• Publisher ads includes LH as a dependency, and you're expected to clone their repo and run their CLI: node index.js <url>
• Treo's field perf has LH as a peer dep and you're expected to create a project and install field-perf as a dep, then do npx lighthouse https://url --plugins=lighthouse-plugin-field-performance

Both of these seem a little backward. Most CLI users are expected to have LH as a global install.

(The situation where we're fine (I think) is when LH is a devDep and people run a yarn lighthouse script... in that case plugins should install (as another devDep) and run just fine.)

But with a global install of Lighthouse... what about plugins... Do you also install them as a global module? If so, the current --plugins= CLI flag doesn't successfully resolve them. If we don't support plugins with a global LH, then we'll need to document it. (but that seems bad).

[denar90]

What I can add here is - it works great if:

• both LH and plugin installed globally
• both of them installed locally

[connorjclark]

We should not allow mixing of global/local installs.

make a repo template for plugins thats new hotness

[paulirish]

Remaining work: add documentation for plugin use as a user.

[brendankenny]

#11696 made the globally installed lighthouse work well now