build: align minimum build dependencies with ndn-cxx

 * Recommend boost >= 1.65.1 and gcc >= 7.4.0
 * Require clang >= 4.0, or Xcode >= 9.0 on macOS
 * Silence an ABI-related diagnostic message from gcc on armv7
 * Fix redundant-tags warning with gcc 10
 * Add CentOS-specific instructions to docs/INSTALL.rst
 * Add Xcode 11.5 to Travis CI

Refs: #5087, #5106
Change-Id: I70746729a132ecb07d4788934385bb403039dba9
diff --git a/docs/index.rst b/docs/index.rst
index 0c5094e..2b6b093 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -40,24 +40,23 @@
 
 **Additional documentation**
 
-* `NFD Developer's Guide <https://named-data.net/wp-content/uploads/2016/10/ndn-0021-7-nfd-developer-guide.pdf>`_
+* `NFD Developer's Guide <https://named-data.net/publications/techreports/ndn-0021-10-nfd-developer-guide/>`__
 
   A comprehensive guide to the design and implementation of NFD. The developer's guide also contains
   suggestions and hints for anyone wanting to modify or extend NFD.
 
-* `NDN Software Contributor's Guide
-  <https://github.com/named-data/NFD/blob/master/CONTRIBUTING.md>`__
+* `NDN Software Contributor's Guide <https://github.com/named-data/.github/blob/master/CONTRIBUTING.md>`__
   (guide for newcomers to the NDN community of software)
 
-* `NFD Wiki <https://redmine.named-data.net/projects/nfd/wiki>`_
+* `NFD Wiki <https://redmine.named-data.net/projects/nfd/wiki>`__
 
-  + `NFD Management protocol <https://redmine.named-data.net/projects/nfd/wiki/Management>`_
-  + `NFD Configuration file format <https://redmine.named-data.net/projects/nfd/wiki/ConfigFileFormat>`_
+  + `NFD Management protocol <https://redmine.named-data.net/projects/nfd/wiki/Management>`__
+  + `NFD Configuration file format <https://redmine.named-data.net/projects/nfd/wiki/ConfigFileFormat>`__
 
   The NFD Wiki contains detailed protocol specifications and
   information for building on unsupported platforms.
 
-* `API Documentation (doxygen) <doxygen/annotated.html>`_
+* `API Documentation (doxygen) <doxygen/annotated.html>`__
 
 * :doc:`RELEASE_NOTES`
 
@@ -66,7 +65,7 @@
 License
 -------
 
-NFD is an open and free software package licensed under GPL 3.0 license and is the
-centerpiece of our committement to making NDN's core technology open and free to all
-Internet users and developers. For more information about the licensing details and
-limitation, refer to `COPYING.md <https://github.com/named-data/NFD/blob/master/COPYING.md>`_.
+NFD is a free and open-source software package licensed under the GPL version 3 and
+is the centerpiece of our committement to making NDN's core technology free and open
+to all Internet users and developers. For more information about licensing, refer to
+`COPYING.md <https://github.com/named-data/NFD/blob/master/COPYING.md>`__.