docs(analyzer): Name precondition for analysis to work

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

website/docs/tools/analyzer.md

@@ -6,7 +6,11 @@ sidebar_position: 1
 
 The *analyzer* is a Software Composition Analysis (SCA) tool that determines the dependencies of software projects inside the specified version-controlled input directory (`-i`).
 It is the only mandatory tool to run from ORT as its output is the input for all other tools.
-It does so by querying the detected package managers; **no modifications** to your existing project source code, like applying build system plugins, are necessary for that to work.
+Analysis works by querying the detected package managers; **no modifications** to your existing project source code, like applying build system plugins, are necessary for that to work if the following preconditions are met:
+
+* All projects use one of the package managers listed below in a reasonably recent version, and they are configured according to common best practices.
+* All projects can be built in a single step out-of-the-box, without any custom confguration being set, like build system properties or environment variables.
+
 The tree of transitive dependencies per project is written out as part of an [OrtResult](https://github.com/oss-review-toolkit/ort/blob/main/model/src/main/kotlin/OrtResult.kt) in YAML (or JSON, see `-f`) format to a file named `analyzer-result.yml` in the specified output directory (`-o`).
 The output file exactly documents the status quo of all package-related metadata.
 It can be further processed or manually edited before passing it to one of the other tools.