add rules for cards without buy or play cost

No buy cost -> can not be bought.
No play cost -> can not be played.

1 files changed, 2 insertions, 0 deletions

diff --git a/rules/en/rules.md b/rules/en/rules.md
index 54ef7c81..da3b21ad 100644
--- a/rules/en/rules.md
+++ b/rules/en/rules.md
@@ -75,6 +75,7 @@ For each of your Units
   * Example: "Whenever the equipped **unit** *attacks* gain 1 **resource**" - "the equipped **unit** *attacks*" is the condition and "gain 1 **resource**" is the *triggered* **action**
 * All game action a player does are **actions**
 * Playing a card is an action, in doing so they must pay the card's **playing cost** as the cost for the **action**
+* Cards without **playing cost** (not cards with `playing cost = 0`) can not be played as an action in this way.
 * Using a **permanent** like **units** are **actions**
 * Actions are processed in two steps:
   * By *declaring* an **action** the player announces the desired effects, all its *targets* and pays all required costs
@@ -122,6 +123,7 @@ While you control an untapped card on the board or have a playable card in hand
 * To buy a card a player pays **resource** equal to the **buy cost** of the card
 * Only one card can be *bought* per turn
 * The *bought* card is put onto the **discard pile**
+* Cards without **buy cost** can not be *bought*
 
 # Deck