Merge pull request #271 from tonivega/feature/trendline-chore

Added additional documentation to the trend lines switch -s

Author: fabianp

README.rst

@@ -218,6 +218,18 @@ Trend lines and its numeric slope can be plotted using the ``s`` flag, such as
 
     mprof plot -s
 
+.. image:: ./images/trend_slope.png
+   :height: 350px
+
+The intended usage of the -s switch is to check the labels' numerical slope over a significant time period for : 
+
+  - ``>0`` it might mean a memory leak.
+  - ``~0`` if 0 or near 0, the memory usage may be considered stable.
+  - ``<0`` to be interpreted depending on the expected process memory usage patterns, also might mean that the sampling period is too small.
+
+The trend lines are for ilustrative purposes and are plotted as (very) small dashed lines.
+
+
 Setting debugger breakpoints
 =============================
 It is possible to set breakpoints depending on the amount of memory used.