docs: expand restic cat documentation (#5679)

Co-authored-by: Michael Eischer <michael.eischer@fau.de>

doc/conf.py

@@ -61,7 +61,16 @@ language = "en"
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This patterns also effect to html_static_path and html_extra_path
-exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']
+exclude_patterns = [
+    '_build',
+    'Thumbs.db',
+    '.DS_Store',
+    # Included only via 100_references.rst (avoids duplicate labels).
+    'design.rst',
+    'view_repository.rst',
+    'cache.rst',
+    'REST_backend.rst',
+]
 
 # The name of the Pygments (syntax highlighting) style to use.
 pygments_style = 'sphinx'