docs: describe intended ways to use Renovate

docs/development/design-decisions.md

@@ -2,6 +2,17 @@
 
 This file documents the design choices as well as configuration options.
 
+## Intended usage by end-users
+
+Renovate is intended to be used as an app.
+It should not be used as a library, because it lacks a stable API.
+
+We do not want to create a stable API, or document our existing API.
+The API and documentation would need a major overhaul each time we refactor our code.
+
+End users should only depend on the CLI or on the official hosted app.
+The Renovate npm package should only be used as a CLI tool.
+
 ## Stateless
 
 A key feature of Renovate is that it does not require any state storage (e.g. on disk or in a database).

docs/usage/faq.md

@@ -39,6 +39,17 @@ The Renovate team will only create bugfixes for an older version if the hosted a
 If you're using the hosted app, you don't need to do anything, as the Renovate maintainers update the hosted app regularly.
 If you're self hosting Renovate, use the latest release if possible.
 
+## Supported ways of using Renovate
+
+Renovate is intended to be used as an app.
+We do not support using Renovate as a library.
+
+Supported ways to use Renovate:
+
+- via the CLI program
+- via the official hosted app
+- via selfhosting the Renovate app
+
 ## Renovate core features not supported on all platforms
 
 | Feature              | Platforms which lack feature                      | See Renovate issue(s)                                        |