GH-41673: [Format][Docs] Add arrow format introductory page

docs/source/format/CanonicalExtensions.rst

@@ -272,6 +272,8 @@ JSON
   In the future, additional fields may be added, but they are not required
   to interpret the array.
 
+.. _uuid_extension:
+
 UUID
 ====
 

docs/source/format/Columnar.rst

@@ -89,6 +89,8 @@ concepts, here is a small glossary to help disambiguate.
   are parametric by construction. A timestamp is also parametric as it needs
   a unit (such as microseconds) and a timezone.
 
+.. _data_types:
+
 Data Types
 ==========
 

docs/source/format/Glossary.rst

@@ -15,6 +15,8 @@
 .. specific language governing permissions and limitations
 .. under the License.
 
+.. _glossary:
+
 ========
 Glossary
 ========