Update py_houghlines.rst

The current code identified only one random line on the example image. This could be confusing for the novice perusing this for their study. Modified the code to detect all the lines in the image

Author: shreedhar-sde

source/py_tutorials/py_imgproc/py_houghlines/py_houghlines.rst

@@ -51,12 +51,13 @@ Everything explained above is encapsulated in the OpenCV function, **cv2.HoughLi
     import cv2
     import numpy as np
 
-    img = cv2.imread('dave.jpg')
+    img = cv2.imread('dave.png')
     gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
     edges = cv2.Canny(gray,50,150,apertureSize = 3)
 
     lines = cv2.HoughLines(edges,1,np.pi/180,200)
-    for rho,theta in lines[0]:
+    for line in lines:
+        rho,theta= line[0]
         a = np.cos(theta)
         b = np.sin(theta)
         x0 = a*rho