#759 add changelog

[martinjrobins]

Description

Adds changelog for #759

Sorry, forgot to add this!

[codecov]

Codecov Report

Merging #817 into master will increase coverage by 0.04%.
The diff coverage is 98.55%.

@@            Coverage Diff             @@
##           master     #817      +/-   ##
==========================================
+ Coverage   98.14%   98.19%   +0.04%     
==========================================
  Files         180      181       +1     
  Lines        9987    10227     +240     
==========================================
+ Hits         9802    10042     +240     
  Misses        185      185

Impacted Files	Coverage Δ
pybamm/expression_tree/exceptions.py	100% <ø> (ø)	⬆️
pybamm/models/submodels/particle/base_particle.py	93.33% <ø> (-3.97%)	⬇️
...dels/submodels/particle/fast/base_fast_particle.py	100% <ø> (ø)	⬆️
pybamm/solvers/casadi_solver.py	100% <100%> (ø)	⬆️
...m/models/full_battery_models/base_battery_model.py	100% <100%> (ø)	⬆️
...odels/full_battery_models/lithium_ion/basic_dfn.py	100% <100%> (ø)	⬆️
...bamm/parameters/standard_parameters_lithium_ion.py	100% <100%> (ø)	⬆️
...ernal_circuit/function_control_external_circuit.py	100% <100%> (ø)	⬆️
...els/submodels/particle/fast/fast_many_particles.py	100% <100%> (ø)	⬆️
...odels/full_battery_models/lithium_ion/basic_spm.py	100% <100%> (ø)	⬆️
... and 18 more

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[valentinsulzer]

We have been referring to pull requests rather than issues in the changelog

[martinjrobins]

We have been referring to pull requests rather than issues in the changelog

I'm happy to change this, but note that this particular breaking change was documented in the issue, not the PR.

[valentinsulzer]

oh right, good point, leave as is then. Thanks!