Update Prerequisites.Rmd

Prerequisites.Rmd

@@ -91,7 +91,7 @@ Then try the `install_github` command again.
   - You may need to install X11 from [http://www.xquartz.org](http://www.xquartz.org). 
   - If you get an error about package `stringi` try typing `install.packages('stringi',type='mac.binary')`. Then re-run the commands above
   <!-- - If you get some errors about `pandoc` when installing simmr leave out the `build_vignettes=TRUE` argument -->
-    - related to the installation of the command line tools, you may get errors such as `make: gfortran: no such file or directory mac` which relate to missing information for the calling of C++ and FORTRAN compilers. The solution is to download and [install the required GFORTRAN](https://thecoatlessprofessor.com/programming/cpp/r-compiler-tools-for-rcpp-on-macos/) libraries. The instructions here are not very clear so take your time working through them. **N.B. Again for M1/M2 chip owners, you will have to do something different as the latest version of gfortran is not available through this route - see next step.**
+    - related to the installation of the command line tools, you may get errors such as `make: gfortran: no such file or directory mac` which relate to missing information for the calling of C++ and FORTRAN compilers. The solution is to download and [install the required GFORTRAN](https://thecoatlessprofessor.com/programming/cpp/r-compiler-tools-for-rcpp-on-macos/) libraries. The instructions here are not very clear so take your time working through them. **N.B. Again for M1/M2 chip owners, you will have to do something different as the latest version of gfortran is not available through this route - see next step**
       - For M1/M2 users, you will need to use Homebrew which is a package and software manager for OSX. First install [homebrew](https://brew.sh). Then open the OSX Terminal (there is also a Terminal pane in Studio you can use) and type `brew upgrade` and press return, followed by `brew update` and again return. Now you can `brew install gcc`. The final step is you will need to point R to your gcc installation of gfortran. This is achieved by creating a Makevars file and putting in a new folder in your home directory called "~/.R". You can create this hidden folder by opening a Terminal and typing `mkdir -p ~/.R`. You can then copy the "Makevars" file from this course's repository in the folder "osx_cpp_fortran_installation" and paste it into your "~/.R" folder. Alternatively you can create it yourself and paste the following text into it
 
 ```