[packages] Improvide conf documentation

- about LOCALE packages
 - about pre- and post-scripts

CC: #1057

src/modules/packages/packages.conf

@@ -89,20 +89,25 @@ update_system: false
 # "package: vi" with neither script option will trick Calamares into
 # trying to install a package named "package: vi", which is unlikely to work.
 #
+# Pre- and post-scripts are supported only in the install and try_install
+# operations.
+#
 # Any package name may be localized; this is used to install localization
 # packages for software based on the selected system locale. By including
-# the string LOCALE in the package name, the following happens:
+# the string `LOCALE` in the package name, the following happens:
 #
 # - if the system locale is English (any variety), then the package is not
 #   installed at all,
-# - otherwise $LOCALE or ${LOCALE} is replaced by the 'lower-cased' BCP47
+# - otherwise `$LOCALE` or `${LOCALE}` is replaced by the 'lower-cased' BCP47
 #   name of the 'language' part of the selected system locale (not the
 #   country/region/dialect part), e.g. selecting "nl_BE" will use "nl"
 #   here.
 #
-# Take care that just plain LOCALE will not be replaced, so foo-LOCALE will
-# be left unchanged, while foo-$LOCALE will be changed. However, foo-LOCALE
-# 'will' be removed from the list of packages, if English is selected.
+# Take care that just plain `LOCALE` will not be replaced, so `foo-LOCALE` will
+# be left unchanged, while `foo-$LOCALE` will be changed. However, `foo-LOCALE`
+# **will** be removed from the list of packages (i.e. not installed), if 
+# English is selected. If a non-English locale is selected, then `foo-LOCALE`
+# will be installed, unchanged (no language-name-substitution occurs).
 #
 # The following installs localizations for vi, if they are relevant; if
 # there is no localization, installation continues normally.