Bug 14674: [QA Follow-up] Typos and textual adjustment

Bug 14674: [QA Follow-up] Typos and textual adjustment

This patch does:

[1] Resolve error [koha-create: line 294: local: `=upload21': not a valid
    identifier] by replacing $instance by instance.
[2] Resolved typo for 'specify'.
[3] Resolve error: [sed: -e expression #26, char 20: unknown option to `s']
    by replacing the slash in the sed line by a #. This makes sed not
    stumble over the slashes in the upload path.
[4] Added the aspect of permanent storage in the wording (as opposed to
    the storage of temporary uploads in /tmp or similar).

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Verified that koha-create now inserts the right path in koha-conf.xml.
Verified that koha-create-dirs created the new uploads directory.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>