build: align minimum build dependencies with ndn-cxx
* Recommend gcc >= 7.4.0
* Require clang >= 4.0, or Xcode >= 9.0 on macOS
* Silence an ABI-related diagnostic message from gcc on armv7
* Make graphviz optional for building documentation
* Sync sphinx configuration
Change-Id: Iff1920b0b5580d58db9aeef11298f11e22d9b3cb
diff --git a/docs/INSTALL.rst b/docs/INSTALL.rst
index 771a07c..35cd53b 100644
--- a/docs/INSTALL.rst
+++ b/docs/INSTALL.rst
@@ -1,7 +1,5 @@
-.. _NDNS Installation Instructions:
-
-NDNS Installation Instructions
-==============================
+Installation Instructions
+=========================
Prerequisites
-------------