added temporary variable usage document

Author: Cerem Cem ASLAN

doc/Ractive/temporary-variables-inside-each-loop.ls

@@ -0,0 +1,22 @@
+'''
+Temporary Variable inside an `each` loop: 
+
+        {{#each myobj}}
+            {{ @context.set('._tmp1', (.foo !== 'bar')) && '' }}
+            ...
+        {{/each}}
+
+or by using `<tmp />` component:
+
+        {{#each myobj}}
+            <tmp key="._tmp1" value="{{.foo !== 'bar'}}" /> 
+            ...
+        {{/each}}
+
+'''
+Ractive.components['tmp'] = Ractive.extend do 
+    template: ''
+    isolated: no 
+    on:
+        init: (ctx) -> 
+            ctx.set @get('key'), @get('value')