Fixed add period docs

docs/administrator/add_course.rst

@@ -26,8 +26,10 @@ To create a new course tag click the **Add Tag** in the upper right corner.
 Type the name and set the category to **Course** and click save.
 
 Finally set the period tag by clicking the magnifier icon next to the **Active Period:** field.
-Choose an existing tag if it's already defined otherwise click **Add Tag** and type the info.
+Choose an existing tag if it's already defined otherwise click **Add Tag** [#periodtag]_ and type the info.
 
 .. image:: ../images/add_period_tag.png
 
-Click save.
+Click save.
+
+.. [#periodtag] A period is a tag with a special category that act as a period. The active period is just one of the defined period tags making it possible to easily switch between periods.

docs/administrator/add_period.rst

@@ -0,0 +1,17 @@
+################
+Add a new period
+################
+
+A period is implemented within the tag system. This means that a period is only a tag with a particular category.
+In practice a course is defined by its course and period tag. Making it the default activated tags when the assignments
+are presented to the students within the boundaries of a course. This is how trix have mirrored the real world course structure.
+
+.. image:: ../images/djangoadmin_frontpage.png
+
+To add a new period tag click the **Tags** item in the list.
+
+.. image:: ../images/tags_list.png
+
+Click **Add Tag** in the upper right corner and then type the name of the tag along with the category *Period*
+
+The newly added period tag can then be defines as the active period on a course.

docs/administrator/index.rst

@@ -8,5 +8,6 @@ Trix administrator documentation
 
    gettingstarted
    administer_course
+   add_period
    add_course
    add_admin