Adding docs for == to trunk.

git-svn-id: svn://hamptoncatlin.com/haml/trunk@495 7063305b-7217-0410-af8c-cdc13e5119b9

lib/haml.rb

@@ -538,6 +538,20 @@ $LOAD_PATH << dir unless $LOAD_PATH.include?(dir)
 #     yo
 #   </p>
 #
+# You can also use two equal signs, <tt>==</tt>,
+# along with conventional Ruby string-embedding syntax
+# to easily embed Ruby code in otherwise static text.
+# For example:
+#
+#   %p
+#     == 1 + 1 = #{1 + 1}
+#
+# is compiled to:
+#
+#   <p>
+#     1 + 1 = 2
+#   </p>
+# 
 # ==== -
 # 
 # The hyphen character makes the text following it into "silent script":