added 9.29 and 9.30

ch09/README.md

@@ -192,3 +192,19 @@ void insert(forward_list<string> &flst, string find, string insrt)
     flst.insert_after(prev, insrt);
 }
 ```
+
+## Exercise 9.29:
+>Given that vec holds 25 elements, what does
+vec.resize(100) do? What if we next wrote vec.resize(10)?
+
+```cpp
+vec.resize(100);    // adds 75 elements of value 0 to the back of vec
+vec.resize(10);     // erases 90 elements from the back of vec
+```
+
+## Exercise 9.30:
+>What, if any, restrictions does using the version of resize
+that takes a single argument place on the element type?
+
+If the container holds elements of a class type and resize adds elements
+we **must supply an initializer** or the element type must have a **default constructor**.