update jax shape discussion (#413)

Author: HumphreyYang

lectures/jax_intro.md

@@ -274,12 +274,18 @@ for A in matrices:
     print(A)
 ```
 
-One point to remember is that JAX expects tuples to describe array shapes, even for flat arrays.  Hence, to get a one-dimensional array of normal random draws we use `(len, )` for the shape, as in
+To get a one-dimensional array of normal random draws, we can either use `(len, )` for the shape, as in
 
 ```{code-cell} ipython3
 random.normal(key, (5, ))
 ```
 
+or simply use `5` as the shape argument:
+
+```{code-cell} ipython3
+random.normal(key, 5)
+```
+
 ## JIT compilation
 
 The JAX just-in-time (JIT) compiler accelerates logic within functions by fusing linear