Add more sections in README

Author: Atry

README.md

@@ -199,6 +199,52 @@ By combining pure `Tensor`s along with the impure `cache` mechanism, we achieved
 
 ### Scala collection interoperability
 
+#### `split`
+
+A `Tensor` can be `split` into small `Tensor`s on the direction of a specific dimension.
+
+For example, given a 3D tensor whose `shape` is 2x3x4,
+
+``` scala
+val my3DTensor = Tensor((0.0f until 24.0f by 1.0f).grouped(4).toSeq.grouped(3).toSeq)
+
+val Array(2, 3, 4) = my3DTensor.shape
+```
+
+when `split` it at the dimension #0, 
+
+``` scala
+val subtensors0 = my3DTensor.split(dimension = 0)
+```
+
+then the result should be a `Seq` of two 3x4 tensors.
+
+``` scala
+// Output: TensorSeq([[0.0,1.0,2.0,3.0],[4.0,5.0,6.0,7.0],[8.0,9.0,10.0,11.0]], [[12.0,13.0,14.0,15.0],[16.0,17.0,18.0,19.0],[20.0,21.0,22.0,23.0]])
+println(subtensors0)
+```
+
+When `split` it at the dimension #1, 
+
+``` scala
+val subtensors1 = my3DTensor.split(dimension = 1)
+```
+
+then the result should be a `Seq` of three 2x4 tensors.
+
+``` scala
+// Output: TensorSeq([[0.0,1.0,2.0,3.0],[12.0,13.0,14.0,15.0]], [[4.0,5.0,6.0,7.0],[16.0,17.0,18.0,19.0]], [[8.0,9.0,10.0,11.0],[20.0,21.0,22.0,23.0]])
+println(subtensors1)
+```
+
+Then you can use arbitrary Scala collection functions on Seq of subtensors.
+
+#### `join`
+
+TODO
+
+#### Fast matrix multiplication from `split` and `join`
+
 TODO
 
 ## Benchmark