[docs] Put an explicit link to InAlloca.rst

llvm-svn: 228192
diff --git a/llvm/docs/index.rst b/llvm/docs/index.rst
index dd6ea18..65857cd 100644
--- a/llvm/docs/index.rst
+++ b/llvm/docs/index.rst
@@ -343,6 +343,9 @@
 :doc:`MergeFunctions`
   Describes functions merging optimization.
 
+:doc:`InAlloca`
+  Description of the ``inalloca`` argument attribute.
+
 Development Process Documentation
 =================================