added np.chars

Author: Oceania2018

README.md

@@ -40,9 +40,9 @@ The NumPy class is a high-level abstraction of NDArray that allows NumSharp to b
 
 ### How to use
 ```cs
-// init NumPy instance which pesists integer data type
-var np = new NumPy();
-
+using np = NumSharp.Core.NumPy;
+```
+```cs
 // create a vector
 var nd = np.arange(12)
 

src/NumSharp.Core/NumPy.cs

@@ -15,6 +15,7 @@ public static partial class NumPy
         public static Type int64 => typeof(Int64);
         public static Type float32 => typeof(float);
         public static Type float64 => typeof(double);
+        public static Type chars => typeof(string);
 
         public static NumPyRandom random => new NumPyRandom();
     }