replace pdf with png

docs/decision-tree.md

@@ -7,20 +7,20 @@
 
 <a name="ethics-rdm"></a>
 ## Process 1
-![](../img/p1.pdf)
+![](../img/p1.png)
 
 <a name="protected"></a>
 ## Process 2
-![](../img/p2.pdf)
+![](../img/p2.png)
 
 <a name="deidentify"></a>
 ## Process 3
-![](../img/p3.pdf)
+![](../img/p3.png)
 
 <a name="metadata"></a>
 ## Process 4
-![](../img/p4.pdf)
+![](../img/p4.png)
 
 <a name="sharing-attribution"></a>
 ## Process 5
-![](../img/p5.pdf)
+![](../img/p5.png)