Update introduction.rst

docs/introduction.rst

@@ -29,7 +29,7 @@ and install the latest stable version:
 The :mod:`-e` is optional and will install the project in developer (editable) mode.
 
 For the code to generate VASP input files along with the surface slabs, 
-`pymatgen POTCAR environment <https://pymatgen.org/installation.html#potcar-setup>`
+`pymatgen POTCAR environment <https://pymatgen.org/installation.html#potcar-setup>`_
 must be set up correctly. 
 
 =====
@@ -43,4 +43,4 @@ Take a look at our `command line interface (CLI) examples <command_line_examples
 of the CLI tools available. 
 
 There is full documentation for all modules (have a browse of the side bar on the left)  
-if you would rather use the python API directly. 
+if you would rather use the python API directly.