Fix #2615: Document literal singleton types

Author: Varunram

docs/docs/reference/singleton-types.md

@@ -3,37 +3,19 @@ layout: doc-page
 title: "Literal Singleton Types"
 ---
 
-Singleton types is one of the most popular features in Scala. Literal Singleton types takes it a step further.
-Right now, a popular way to replicate literal singleton types is to create macros and/or use libraries such as
-`shapeless` due to the lack of a syntax to express them.
-
-With Literal Singelton types, it is possible to do something like
+Literal Singleton Types allows primitive literals to be used as types. For example:
 
 ```scala
 val t: "Jedi".type = "Jedi"
-```
-or
-```scala
 val t: 42.type = 42
-```
-or
-```scala
 val t: 42 = 42
 ```
 
-to use literal Singleton types. Trying to do the same in Scala produces the following error:
-```
-<console>:1: error: identifier expected but string literal found.
-val t: "Jedi".type = "Jedi"
-```
+It is also possible to define functions returning or taking singleton types such as
 
-Dotty provides support for using Literal Singleton types of the last format namely:
 ```scala
-val t: 42 =42
-val x: "Jedi" = "Jedi"
+def f(t: Double): t.type = t
+val a: 1.2 = f(1.2)
 ```
-and so on.
-
-There is a possibility to use singleton types in some contexts, but only on identifiers which points to a constant that conforms to `AnyRef`. This restriction is due to `Any` not having an eq method, which is what’s used for singleton type-equality check and pattern matching.
 
 For more details and the motivation behind the need for literal singleton types, check out [SIP-23](http://docs.scala-lang.org/sips/pending/42.type.html)