Fix minor header wordings

This commit fixes minor header wordings which were mentioned in the
previous patch review[1].

[1] Ia1e8e16e5f5ddb06e4c4ccb4979b0750b88a4db4

Change-Id: I4db09bda5628371186e3548143c59d0841fcb7b0
diff --git a/doc/source/index.rst b/doc/source/index.rst
index c4affd2..f562850 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -24,8 +24,8 @@
    field_guide/scenario
    field_guide/unit_tests
 
-For users
-=========
+Users Guide
+===========
 
 Tempest Configuration Guide
 ---------------------------
@@ -48,8 +48,8 @@
    workspace
    run
 
-For developers
-==============
+Developers Guide
+================
 
 Development
 -----------