doc: notes: rework --[no-]stripspace

doc: notes: rework --[no-]stripspace

Document this option by copying the bullet list from git-stripspace(1).
A bullet list is cleaner when there are this many points to consider.
We also get a more standardized description of the multiple-blank-lines
behavior.  Compare the repeating (git-notes(1)):

    empty lines other than a single line between paragraphs

With (git-stripspace(1)):

    multiple consecutive empty lines

And:

    leading [...] whitespace

With:

    empty lines from the beginning

Leading whitespace in the form of spaces (indentation) are not removed.
However, empty lines at the start of the message are removed.

Note that we drop the mentions of comment line handling because they are
wrong; this option does not control how lines which can be recognized as
comment lines are handled.  Only interactivity controls that:

• Comment lines are stripped after editing interactively
• Lines which could be recognized as comment lines are left alone when
  the message is given non-interactively

So it is misleading to document the comment line behavior on
this option.

Further, the text is wrong:

    Lines starting with `#` will be stripped out in non-editor cases
    like `-m`, [...]

Comment lines are still indirectly discussed on other options.  We will
deal with them in the next commit.

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>