Update note about JDT with 3rd party compiler backend (#2813)

Co-authored-by: Ed Merks <[email protected]>

eclipse.platform.common/bundles/org.eclipse.jdt.doc.user/reference/ref-jdt-faq.htm

@@ -25,13 +25,14 @@ <h3>
       With the Workbench?
     </h3>
     <p>
-
-      No. The JDT provides a number of sophisticated features including fully
-      automatic incremental compilation, code snippet evaluation, code assist,
-      type hierarchies, and hot code replace. These features require special
-      support found in the workbench Java compiler (an integral part of the
-      JDT's incremental project builder), but not available in standard Java
-      compilers.
+      Not with vanilla JDT. Some features of JDT such as Snippet evaluation do require usage
+      of the built-in compiler and currently cannot work with another compiler.
+    </p>
+    <p>
+      However, note that JDT does provide some mechanisms to allow 3rd-party plugins to
+      enable an external compiler instead of the built-in one for most features (completion,
+      selection, search, incremental compilation, and so on) but actual usage of such third-party
+      compilers is not something that JDT includes nor for which JDT is responsible.
     </p>
     <h3>
       Where Do Java Packages Come From?