fix remaining links in docs

Author: hotzenklotz

docs/src/webknossos-py/examples/merge_nmls.md

@@ -1,7 +1,7 @@
 # Merge Trees of two NML files
 
-This example opens two [NML files](/webknossos/data/concepts.md#nml-files) and copies the trees from the NML A to B and saves the output to a new NML (that includes the trees of both input NMLs).
-This example opens two [NML files](/webknossos/data/concepts.md#nml-files) and copies the trees from the NML A to B and saves the output to a new NML (that includes the trees of both input NMLs).
+This example opens two [NML files](/webknossos/data/concepts.html#nml-files) and copies the trees from the NML A to B and saves the output to a new NML (that includes the trees of both input NMLs).
+This example opens two [NML files](/webknossos/data/concepts.html#nml-files) and copies the trees from the NML A to B and saves the output to a new NML (that includes the trees of both input NMLs).
 
 ```python
 --8<--

webknossos/webknossos/skeleton/skeleton.py

@@ -15,7 +15,7 @@
 @attr.define
 class Skeleton(Group):
     """
-    Representation of the [skeleton](/webknossos/skeleton_annotation.html) of an `Annotation`.
+    Representation of the [skeleton](/webknossos/skeleton_annotation/index.html) of an `Annotation`.
     It contains metadata to identify the related dataset and is the root-group of sub-groups and trees.
     See the parent class `Group` for methods about group and tree handling.
     To upload a skeleton to webknossos, please create an `Annotation()` with it.