Fix RT priority docs (NFC) (#3098)

The ranges and which value was specified as highest were incorrect on
some of them. On Linux, the range is 1 to 99 with 99 being highest.

From `man 7 sched`:
```
Processes scheduled under one of the real-time policies (SCHED_FIFO,
SCHED_RR) have a sched_priority value in the range 1 (low) to 99 (high).
```

Also clean up the relevant javadoc and doxygen comments.

wpilibc/src/main/native/include/frc/Notifier.h

@@ -46,8 +46,9 @@ class Notifier : public ErrorBase {
    * This is useful for reducing scheduling jitter on processes which are
    * sensitive to timing variance, like model-based control.
    *
-   * @param priority The FIFO real-time scheduler priority ([0..100] where a
-   *                 lower number represents higher priority).
+   * @param priority The FIFO real-time scheduler priority ([1..99] where a
+   *                 higher number represents higher priority). See "man 7
+   *                 sched" for more details.
    * @param handler  The handler is called at the notification time which is set
    *                 using StartSingle or StartPeriodic.
    */