Elaborate more on -native-build-target

Author: Zeta611

README.md

@@ -138,7 +138,9 @@ This automatically annotates `@live` all the items in the `src/test` and `tmp` f
 
 ### CLI -native-build-target
 
-If a native project uses code generation, e.g., via `ocamlyacc`, the build target path needs to be specified to ensure correct analysis.
+If a native project uses code generation and emit the generated files only in the build directory, reanalyze may not be able to locate them.
+This is due to the paths being not relative to the project root directory.
+An example of it can be caused by using tools like `ocamlyacc`.
 
 For example, you might want to set `_build/default` for projects that use the default dune build target:
 ```sh