tools/memory-model: docs/simple.txt: Fix trivial typos

Lockless programming is considered by many to be more difficult than

lock-based programming, but there are a few lockless design patterns that

have been built out into an API.  One of these APIs is sequence locking.

Although this APIs can be used in extremely complex ways, there are simple

Although this API can be used in extremely complex ways, there are simple

and effective ways of using it that avoid the need to pay attention to

memory ordering.

operations from the previous section only when there are no racing

accesses.  Otherwise, use only fully ordered operations when accessing

or modifying the variable.  This approach guarantees that code prior

to a given access to that variable will be seen by all CPUs has having

to a given access to that variable will be seen by all CPUs as having

happened before any code following any later access to that same variable.

Please note that per-CPU functions are not atomic operations and