Add exercise assignment for Array slicing

Author: mlouhivu

numpy/array-slicing/README.md

@@ -0,0 +1,15 @@
+## Array slicing
+
+First, create a 4x4 array with arbitrary values, then
+
+1. Extract every element from the second row.
+2. Extract every element from the third column.
+3. Assign a value of 0.21 to upper left 2x2 subarray.
+
+Next, create a 8x8 array with checkerboard pattern, i.e. alternating zeros
+and ones:
+
+  1 0 1 ...
+  0 1 0 ...
+  1 0 1 ...
+   ...