First major update of src/2_coordinates.md

src/2_coordinates.md

@@ -358,7 +358,7 @@ We have discussed four different coordinate systems:
 2.  !!! tip "Polar coordinates" 
     $${\bf r} = (r, \phi).$$ This system can be used in two
     dimensions. It is particularly suitable for systems with circular symmetry or functions
-    given in terms of these coordinates.
+    given in terms of these coordinates. \\
     Infinitesimal distance: $$ds^2 = dr^2 + r^2 d\phi^2.$$
     Infinitesimal area: $$dA = r dr d\varphi.$$