Update docs re global.crypto

doc/API.html

@@ -672,12 +672,14 @@ a.equals(b)                    // true</pre>
     <p>
       If the value of <code>this</code> Decimal constructor's
       <a href='#crypto'><code>crypto</code></a> property is <code>true</code>, and the
-      <code>crypto</code> object is available in the host environment, the random digits of the
-      return value are generated by either <code>crypto.getRandomValues</code> (Web Cryptography API
-      in modern browsers) or <code>crypto.randomBytes</code> (Node.js), otherwise, if the the value
-      of the property is <code>false</code> the return value is generated by
+      <code>crypto</code> object is available globally in the host environment, the random digits of
+      the return value are generated by either <code>crypto.getRandomValues</code> (Web Cryptography
+      API in modern browsers) or <code>crypto.randomBytes</code> (Node.js), otherwise, if the the
+      value of the property is <code>false</code> the return value is generated by
       <code>Math.random</code> (fastest).
     </p>
+    <p>To make the <code>crypto</code> object available globally in Node.js use</p>
+    <pre>global.crypto = require('crypto')</pre>
     <p>
       If the value of <code>this</code> Decimal constructor's
       <a href='#crypto'><code>crypto</code></a> property is set <code>true</code> and the
@@ -693,7 +695,6 @@ Decimal.random()                    // '0.4117936847'
 Decimal.random(20)                  // '0.78193327636914089009'</pre>
 
 
-
     <h5 id="Dround">round<code class='inset'>.round(x) <i>&rArr; Decimal</i></code></h5>
     <p><code>x</code>: <i>number|string|Decimal</i></p>
     <p>See <code><a href='#round'>round</a></code>.</p>
@@ -1097,7 +1098,11 @@ Decimal.modulo                     // 9</pre>
       used.
     </p>
     <p>See <a href='#Drandom'><code>random</code></a>.</p>
-    <pre>Decimal.crypto                     // false
+    <pre>
+// Node.js
+global.crypto = require('crypto')
+
+Decimal.crypto                     // false
 Decimal.set({ crypto: true })
 Decimal.crypto                     // true</pre>