Update index.md

Author: amjjbonvin

education/HADDOCK3/HADDOCK3-antibody-antigen/index.md

@@ -203,7 +203,7 @@ Unziping the file will create the `HADDOCK3-antibody-antigen` directory which sh
 
 In case of a workshop of course, HADDOCK3 will usually have been installed on the system you will be using.
 
-In case HADDOCK3 is not pre-installed in your system you will have to install it.
+In case HADDOCK3 is not pre-installed in your system, you will have to install it.
 To obtain HADDOCK3, fill the [registration form](https://docs.google.com/forms/d/e/1FAIpQLScDcd0rWtuzJ_4nftkDAHoLVwr1IAVwNJGhbaZdTYZ4vWu25w/viewform?){:target="_blank"},  navigate to [its repository][haddock-repo]{:target="_blank"}, and then follow the [installation instructions](https://www.bonvinlab.org/haddock3-user-manual/install.html){:target="_blank"}.
 
 In this tutorial we will use the PyMOL molecular visualisation system. If not already installed, download and install PyMOL from [here](https://pymol.org/){:target="_blank"}. You can use your favourite visualisation software instead, but be aware that instructions in this tutorial are provided only for PyMOL.