I am new to spacemacs. I want to install the shell layer. The official page of spacemacs regarding the layer, https://github.com/syl20bnr/spacemacs/tree/master/layers/%2Btools/shell, says
To use this configuration layer, add it to your ~/.spacemacs. You will need to add shell to the existing dotspacemacs-configuration-layers list in this file.
I just don't see how to realize this step. In my .spacemacs file, I have uncommented these lines: