docs: move introduction sentence

docs/internals.rst

@@ -4,9 +4,8 @@
 Internals
 =========
 
-This page documents the internal data structures and storage
-mechanisms of |project_name|. It is partly based on `mailing list
-discussion about internals`_ and also on static code analysis.
+The internals chapter describes and analyses most of the inner workings
+of Borg.
 
 Borg uses a low-level, key-value store, the :ref:`repository`, and
 implements a more complex data structure on top of it, which is made

docs/internals/data-structures.rst

@@ -6,6 +6,10 @@
 Data structures and file formats
 ================================
 
+This page documents the internal data structures and storage
+mechanisms of Borg. It is partly based on `mailing list
+discussion about internals`_ and also on static code analysis.
+
 .. todo:: Clarify terms, perhaps create a glossary.
           ID (client?) vs. key (repository?),
           chunks (blob of data in repo?) vs. object (blob of data in repo, referred to from another object?),