(DOCSP-4993): add clarifying language about time series use case for line and area charts (#264)

Author: jwilliams-mongo

source/chart-type-reference/line-area-chart.txt

@@ -17,9 +17,9 @@ points connected by straight line segments. In area charts, the
 space beneath the line segments is filled in with color, whereas in
 line charts only the line segments are rendered with no additional
 coloring or shading. These charts facilitate visualizing data over a
-period of time and identifying trends and patterns across the entire
-data range. Line and area charts support visualizing both
-:ref:`discrete <discrete-charts>` and :ref:`continuous
+period of time (using time series data) and identifying trends and 
+patterns across the entire data range. Line and area charts support 
+visualizing both :ref:`discrete <discrete-charts>` and :ref:`continuous
 <continuous-charts>` data.
 
 .. _discrete-charts:
@@ -315,8 +315,8 @@ group of 5 years.
    fields, see :ref:`Multiple Field Mappings
    <multiple-field-mappings>`.
 
-Continuous Line Chart
-~~~~~~~~~~~~~~~~~~~~~
+Continuous Line Chart Using Time Series Data
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The following chart visualizes data pertaining to the usage of a
 solar-powered house battery. This continuous line graph shows the