docs: Adding installation instructions and configuration tips

README.md and INSTALL.md now redirect to documentation in docs/ folder.
Later we will add links to HTML pages with NFD documentation.

Change-Id: I4f02f3166e7802570b24ed225ac4de8c56c6e64e
Refs: #1446
diff --git a/docs/index.rst b/docs/index.rst
index 6bc1fff..385a657 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -1,9 +1,11 @@
 NFD - Named Data Networking Forwarding Daemon's documentation
 =============================================================
 
-Contents:
-
 .. toctree::
    release_notes
+   Installation Instruction <INSTALL>
+   NFD Configuration Tips <README>
    manpages
-   :maxdepth: 2
+   :maxdepth: 1
+
+* `API documentation (doxygen) <doxygen/annotated.html>`_