meson: Re-order the optional components

Re-order the optional components to make them alphabetical, and fix up
the indentation to use two spaces as required by meson. A comment is
added to highlight that these optional components are enabled by
default.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

meson.build

@@ -29,12 +29,15 @@ subdir('include')
 subdir('src')
 subdir('utils')
 
-if get_option('tests')
-	subdir('test')
-endif
+# The documentation and test components are optional and can be disabled
+# through configuration values. They are enabled by default.
 
 if get_option('documentation')
-	subdir('Documentation')
+  subdir('Documentation')
+endif
+
+if get_option('tests')
+  subdir('test')
 endif
 
 pkg_mod = import('pkgconfig')