Read position of extremum from shapefile

Instead of asking the user to define it.

Inst_eddies/Tests/test_mean_speed.py

@@ -51,9 +51,10 @@ values_x = interpolate.interpn((lat_rad, lon_rad), values, xi)
 ui = values_x[:, 0]
 vi = values_x[:, 1]
 
-lon_0 = float(input("longitude extremum = ? "))
-lat_0 = float(input("latitude extremum = ? "))
-
+with shapefile.Reader("SHPC/extremum") as sf:
+    p = sf.shape(0)
+    
+lon_0, lat_0 = p.points[0]
 lon_0_rad = lon_0 * np.pi/180
 lat_0_rad = lat_0 * np.pi/180