Improved error msgs and checks in MotteKit installer

scripts/mottekit/install.sh

@@ -7,21 +7,28 @@ readonly mottekit_dir=~/.mottekit
 [ -e "$mottekit_dir" ] &&
     { echo "The $mottekit_dir directory already exists" >&2; exit 1; }
 
-for i in ~/.local/bin ~/bin; do
+path_dirs=(~/.local/bin ~/bin)
+
+for i in "${path_dirs[@]}"; do
     [ "$PATH" = "$i" ] || [[ "$PATH" = *:"$i":* ]] ||
         [[ "$PATH" = "$i":* ]] || [[ "$PATH" = *:"$i" ]] &&
         { entrypoint=$i/mottekit; break; }
 done
 
 [ -z "$entrypoint" ] && {
     echo 'Cannot find a location in PATH suitable for installing the' \
-        'MotteKit entrypoint' >&2
+        'MotteKit entrypoint. You must have one of the following' \
+        'directories in your PATH:' >&2
+    echo "${path_dirs[@]@Q}" >&2
     exit 1
 }
 
 [ -e "$entrypoint" ] &&
     { echo "The entrypoint $entrypoint already exists" >&2; exit 1; }
 
+command -v git >/dev/null ||
+    { echo 'The git command is required but cannot be found' >&2; exit 1; }
+
 echo "Creating the MotteKit directory $mottekit_dir"
 mkdir "$mottekit_dir"