Document how to fix site slowness

[rosiel]

A slow repository system (in search, etc) is frustrating. Can we document some ways that we've found to work to solve this?

• caching : how to configure caching good! i.e. in a way that doesn't break views, etc (not sure if this is a problem in 8, it was in 7).
• if we can use this, 'dont do entity loads on solr results pages' might be useful: https://www.drupal.org/docs/8/modules/search-api-solr/search-api-solr-howtos/create-a-search-view-that-doesnt-load
• css/js caching
• server configs, etc.
• things that might be going on in your browser...
• etc.

Can we document what kinds of tools can help diagnose these issues?

and which IG/ slack channel to ask questions to the folks who know this stuff?