[DOCS] #4587 – Make Sphinx warnings break docs build

Prevent warnings of type "checking consistency... WARNING: document isn't included in any toctree" by using the :orphan: directive.

docs/book.rst

@@ -1,3 +1,5 @@
+:orphan:
+
 .. include:: global.rst.inc
 
 Borg documentation
@@ -15,5 +17,9 @@ Borg documentation
     usage
     deployment
     faq
+    support
+    resources
+    changes
     internals
     development
+    authors

docs/man_intro.rst

@@ -1,3 +1,5 @@
+:orphan:
+
 SYNOPSIS
 --------
 

docs/usage/borgfs.rst

@@ -1 +1,3 @@
+:orphan:
+
 .. include:: borgfs.rst.inc