Add comments to `linkup` and `show-versions`

Readability for the win.

bin/linkup

@@ -10,6 +10,11 @@ tgt=${2:?$usage}
 bak=~/.backup
 
 [[ ! -d $bak ]] && mkdir $bak
+
+# Check if the desired link already exists.
 [[ -L "$tgt" && "$(readlink $tgt)" = "$src" ]] && exit
+
+# Move an existing file to the back up folder.
 [[ -e "$tgt" ]] && mv -v "$tgt" "$bak/${tgt##*/}-$(date '+%Y%m%d-%H%M%S')" || true
+
 ln -sfv "$src" "$tgt"

bin/show-versions

@@ -22,7 +22,9 @@ version_commands=( \
   )
 
 for ver_com in ${version_commands[@]}; do
+  # Get the executable name.
   com=${ver_com%% *}
+  # Report version if executable exists, otherwise report none.
   if [[ -n $(command -v $com) ]]; then
     eval "$ver_com" | head -n 1 || true
   else