Add instruction to fetch Git submodules after cloning

Without fetching Git submodules
(actually, there is only one now, the theme),
Hugo cannot build the website locally due to the missing theme.

Author: dmitry-kabanov

content/howto/member_list.md

@@ -33,7 +33,11 @@ In your terminal/console navigate to a folder where you want to download the rep
 ```bash
 git clone <link> 
 ```
-change into the new folder and switch to a new branch
+then go to the directory of the cloned repository and fetch submodules:
+```bash
+git submodule update --init --recursive
+```
+and switch to a new branch
 ```bash
 git switch --create <branch_name>
 ```