Prepare 5.1.0 release (#1432)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rly

CHANGELOG.md

@@ -1,6 +1,6 @@
 # HDMF Changelog
 
-## HDMF Unreleased
+## HDMF 5.1.0 (March 24, 2026)
 
 ### Enhancements
 - Made `HERDManager` an abstract interface (ABC) with an abstract `external_resources` property. Subclasses must now declare `external_resources` in their `__fields__` to satisfy the interface. Updated `__gather_fields` to allow auto-generated properties to override inherited abstract properties. Added `link_resources` and `get_external_resources` methods to `HERDManager` for managing a linked HERD separate from the primary one. @rly [#1431](https://github.com/hdmf-dev/hdmf/pull/1431)

src/hdmf/container.py

@@ -82,7 +82,7 @@ def get_external_resources(self, linked=False):
 
         Parameters
         ----------
-        linked : bool, optional
+        linked : bool
             If True, return the linked HERD set via ``link_resources``.
             If False (default), return the HERD set via ``__init__`` or the
             ``external_resources`` attribute.