Add paragraph about generic signatures

Author: Duhemm

docs/blog/_posts/2017-11-21-fifth-dotty-milestone-release.md

@@ -37,6 +37,23 @@ Currently two backends that use this frontend are available
 
 Known issues: #3490, #3500.
 
+### Generic java signatures
+Dotty now emits generic signatures for classes and methods. These generic signatures represent the
+signatures before type parameters have been erased. They are used by compilers, debuggers and to
+support reflection.
+
+For instance, it means that the following code now behaves as expected when compiled with Dotty:
+```scala
+class Foo[T, U]
+object Test {
+  def main(args: Array[String]): Unit = {
+    val typeParams = classOf[Foo[_, _]].getTypeParameters
+    println(typeParams.map(_.getName).mkString(", ")) // prints 'T, U'
+  }
+}
+```
+
+Known issues: #3476
 
 ## Trying out Dotty
 ### Scastie