tpm: move documentation under Documentation/security

In order too make Documentation root directory cleaner move the tpm
directory under Documentation/security.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/index.rst b/Documentation/index.rst
index 0058b65..b4c3034 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -19,7 +19,7 @@
    media/dvb-drivers/index
    media/v4l-drivers/index
    gpu/index
-   tpm/index
+   security/index
 
 Indices and tables
 ==================