Update README.md

python/README.md

-make these executable:  
-   chmod +x pcb.py  
-   chmod +x frep.py  
-
-execute:  
-   pcb.py | frep.py  
-
-view:  
-   out.png
-
-optional arguments:  
-   pcb.py | frep.py dpi  
-   pcb.py | frep.py dpi filename  
-
-dependencies:  
-   Python  
-   NumPy  
-   Python Imaging Library  
+pcb.py: FRep PCB design  
+frep.py: FRep pure Python renderer
+frep-C.py: much faster Python+C renderer
 
 sample:
 ![](pcb.png)