Add a pdf version of phs_iteration_schematic

This is needed for the pdf build: latexpdf cannot read svg files.

I converted this using Inkscape (simply using "save as" and saving it as
a pdf).

Author: billsacks

doc/source/tech_note/Plant_Hydraulics/CLM50_Tech_Note_Plant_Hydraulics.rst

@@ -714,6 +714,6 @@ The outermost level of iteration works towards convergence of leaf temperature,
 
 .. _Figure PHS Flow Diagram:
 
-.. figure:: phs_iteration_schematic.svg
+.. figure:: phs_iteration_schematic.*
 
  Flow diagram of leaf flux calculations

doc/source/tech_note/Plant_Hydraulics/README.phs_iteration_schematic

@@ -0,0 +1,9 @@
+Daniel Kennedy provided the original file,
+phs_iteration_schematic.svg. This can be used to generate the html
+documentation. Bill Sacks then converted it to pdf using Inkscape
+(simply using "save as" and saving it as a pdf); the pdf is needed when
+generating a pdf (since latexpdf cannot use svg files).
+
+Note that the figure is referenced in the rst as
+phs_iteration_schematic.*; each builder then uses the appropriate file
+(svg or pdf as needed).