Documentation: RCU: Fix section numbers after adding Section 7 in whatisRCU.rst

Signed-off-by: Wei Zhang <zhangweilst@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Author: zhangweilst

Documentation/RCU/whatisRCU.rst

@@ -59,8 +59,8 @@ experiment with should focus on Section 2.  People who prefer to start
 with example uses should focus on Sections 3 and 4.  People who need to
 understand the RCU implementation should focus on Section 5, then dive
 into the kernel source code.  People who reason best by analogy should
-focus on Section 6.  Section 7 serves as an index to the docbook API
-documentation, and Section 8 is the traditional answer key.
+focus on Section 6 and 7.  Section 8 serves as an index to the docbook
+API documentation, and Section 9 is the traditional answer key.
 
 So, start with the section that makes the most sense to you and your
 preferred method of learning.  If you need to know everything about