Add source control layers

SPC f e d opens the .spacemacs configuration file (M-m f e d Emacs state)

Use / and start typing configuration-layers to search for the dotspacemacs-configuration-layers section. RTN confirms the search text and n jumps to the next occurance, N jumps to the previous occurrence.

Add the following configuration to provide the recommended setup.

     (git :variables
          git-magit-status-fullscreen t)
     github
     (version-control :variables
                      version-control-diff-tool 'diff-hl
                      version-control-global-margin t)