Add link to ode file and add more info to demos

[finsberg]

• Update README with instructions on how to use third-party ODE solver (i.e scipy.integrate.solve_ivp)
• Swap the order of the tutorials so that the tutorial with the Lorentz attractor comes first.
• Add download link to ORdmm_Land.ode file which is used in several demos
• Add source code at the end of the compile-c-extension demo.

Address #115 and #95

[codspeed-hq]

CodSpeed Performance Report

Merging #117 will not alter performance

_{Comparing fix-115 (5b9686d) with main (37c0bfe)}

Summary

✅ 8 untouched benchmarks