prepare release v0.4.0

doc/release_notes.rst

@@ -1,14 +1,18 @@
 Release Notes
 =============
 
-Upcoming Version
-----------------
+.. Upcoming Version
+.. ----------------
+
+Version 0.4.0
+--------------
 
 * When writing out an LP file, large variables and constraints are now chunked to avoid memory issues. This is especially useful for large models with constraints with many terms. The chunk size can be set with the `slice_size` argument in the `solve` function.
 * Constraints which of the form `<= infinity` and `>= -infinity` are now automatically filtered out when solving. The `solve` function now has a new argument `sanitize_infinities` to control this feature. Default is set to `True`.
 * The representation of linopy objects with multiindexed coordinates was improved to be more readable.
 * Grouping expressions is now supported on dimensions called "group" and dimensions that have the same name as the grouping object.
 * Grouping dimensions which have multiindexed coordinates is now supported.
+* See full list of changes `here <https://github.com/PyPSA/linopy/releases/tag/v0.4.0>`__.
 
 Version 0.3.15
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