Add reference for better cross links

Add index index-clamp-installation for crosss reference

Issue-ID: DOC-203

Change-Id: I7f7555f829965982b31aa4baa549cc2709c7d02a
Signed-off-by: Gildas Lanilis <gildas.lanilis@huawei.com>
diff --git a/docs/index.rst b/docs/index.rst
index 50d3127..38044ab 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -70,6 +70,7 @@
 With the default log settings, all logs will be generated into console and into root.log file under the CLAMP root folder. The root.log file is not allowed to be appended, thus restarting the CLAMP will result in cleaning of the old log files.
 
 
+.. _index-clamp-installation:
 
 Installation
 ------------