update tutorial

Author: simongravelle

docs/gromacstutorials-inputs

@@ -0,0 +1 @@
+Subproject commit 726e1de289b1555f432db42581624511a9313a30

docs/sphinx/source/tutorials/level1/protein-in-electrolyte.rst

@@ -17,5 +17,20 @@ Protein in electrolyte
 .. include:: ../../non-tutorials/needhelp.rst
 .. include:: ../../non-tutorials/recommand-salt.rst
 
+Convert the pdb file
+====================
+
+.. container:: justify
+
+    Download the *.pdb* file from the |ProteinDataBank|, or simply
+    click |1cta.pdb|.
+
+.. |ProteinDataBank| raw:: html
+
+    <a href="https://www.rcsb.org/structure/1CTA" target="_blank">Protein Data Bank</a>
+
+.. |1cta.pdb| raw:: html
+
+    <a href="https://raw.githubusercontent.com/gromacstutorials/gromacstutorials-inputs/main/level1/protein-in-electrolyte/1cta.pdb" target="_blank">here</a>
 
 .. include:: ../../non-tutorials/accessfile.rst