This is a follow-up to 366c8a5d94 (PR-15102).
* Documentation/guides/zerolatencyinterrupts.rst
(Title): Make title case consistent.
(Getting Back into the Game, Maskable Nested Interrupts): Clarify discussion
about priorities.
(Cortex-M3/4 Implementation): The first half of a sentence was deleted in
366c8a5d9 because the Kconfig that was described there no longer exists:
CONFIG_ARMV7M_USEBASEPRI. Write a new beginning for this sentence that
matches current implementation.
(Disabling the High Priority Interrupt): Change "cannot" to "must not be
allowed to" to improve clarity.
(Configuring High Priority Interrupts): Change "to NVIC" to "in NVIC" to
improve clarity.
* Documentation/guides/nestedinterrupts.rst:
New. Imported from [1] and converted from CWIKI to reStructuredText.
* Documentation/guides/index.rst:
Link to the new page.
* Documentation/guides/zerolatencyinterrupts.rst:
Replace link to the CWIKI Nested Interrupts page with link to the
above.
[1] https://cwiki.apache.org/confluence/display/NUTTX/Nested+Interrupts
* Documentation/guides/zerolatencyinterrupts.rst:
Add paragraph that defines jitter. Fix a few minor typos. Fix
incorrect reStructuredText formatting for bulletpoints (they were
being rendered like 2nd level bulletpoints).
* Documentation/guides/index.rst:
Add zerolatencyinterrupts.rst to the TOC, which I forgot to do in PR
# 9302.
