✨ feat: add update script

now you can update colorshell by simply running the `update.sh` script :D

scripts/utils.sh

@@ -63,6 +63,20 @@ function Ask() {
     export answer
 }
 
+# -------------
+# Check if colorshell is installed
+# Returns code 0 if installed, 1 if not
+# -------------
+function Is_installed() {
+    executable=${@:-"$HOME/.local/bin/colorshell"}
+
+    if command -v colorshell || [[ -f $executable ]]; then
+        return 0
+    fi
+
+    return 1
+}
+
 # -------------
 # Ask the user to choose a number from the provided list
 # Input answer is exported as $answer