Issue 5521 - Restructure CMS documentation to make it easier to use and extend

docs/structure/settings.md

Index: docs/structure/settings.md
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+# Configuration (settings.ini) #
+
+The following sections can be defined in `settings.ini`:
+
+* `[general]`: following settings should be listed here:
+  * `defaultlocale`: The fallback locale, to be used whenever no localized
+    page/strings can be found for a locale.
+  * `defaultpage`: the default page which is displayed by the server if the URL
+    doesn't contain a page name. Note that while the test server will consider
+    that setting automatically, the real server might need to be configured
+    accordingly.
+  * `crowdin-project-name`: The Crowdin project name, this must be set for if
+    you intend to use the cms.bin.translate script to update the Crowdin
+    translations.
+* `[langnames]`: defines the language names correspoding to particular language
+  codes.
+* `[rtl]`: any language codes listed here are treated as right-to-left languages.
+  The values of the settings are ignored.
+* `[locale_overrides]`: every entry defines that a page should use a different
+  locale file, not the one matching its name (to be used when multiple pages
+  share localization data).