chore: prepare release notes

Author: Midnighter

release-notes/0.15.2.md

@@ -0,0 +1,17 @@
+# Release notes for cobrapy 0.15.2
+
+## New features
+
+* We introduce a new `tolerance` attribute both on the global `Configuration`
+  object as well as `Model`. The default for this is 1E-07. Many functions that
+  use a zero cut-off will now use the set model tolerance value by default.
+  This value can still be set manually via function arguments but attempting to
+  set a threshold that is lower than the model tolerance now raises an error.
+
+## Fixes
+
+* Geometric FBA now has a `processes` argument with a default of 1 which can be
+  used for parallel processing.
+* Clean up the sampling code and make it respect global defaults.
+* Many SBML improvements, please see #835 for details.
+