Added example cron config to keep all local repos up-to-date automatically [ci skip]

lib/git/repo_index.sh

@@ -244,6 +244,8 @@ _git_index_update_all_branches() {
 }
 
 # Updates all git repositories with clean working directories.
+# Use the following cron configuration:
+# */6 * * * * /usr/bin/bash -c '. $HOME/.bashrc && git_index --update-all'
 function _git_index_update_all() {
   echo -e "== Safely updating all local branches in $_bld_col$(_git_index_count)$_txt_col repos...\n"
   _git_index_batch_cmd _git_index_update_all_branches