Update README.md

[jbcaillau]

@ocots for quick review and merge:

• polished a few things
• update the title in Zenodo (modelise -> model)
• same in HAL

Caillau, J.-B., Cots, O., Gergaud, J., Martinon, P., & Sed, S. OptimalControl.jl: a Julia package to model and solve optimal control problems with ODE's [Computer software]. https://doi.org/10.5281/zenodo.13336563

[ocots]

@jbcaillau For the reference, same in:

• bibtex format from README.md
• bibtex
• cff file
• Zenodo metada

[ocots]

Same changes can be made in the

• docs/index.md.

[ocots]

For contributions, update also

•  CONTRIBUTIONS.md.