Update README.md

[arm61]

Description of Work

Fixes #234

Testing Instructions

1. try the new instructions on a macOS machine

[TOFarmer]

New instructions appear to work fine for me.

I assume it is unrelated to this, but the Mantid example script seems to have some problems:

• A large number of the fits fail despite apparently not iterating at all:
  Fit-[Warning] Fit status: Failed to converge after 0 iterations.
• Fits with IkedaCarpenter function (which is neutron wavelength dependent) always reports that the wavelength can't be calculated, and that this can be solved by loading the appropriate instrument:

IFunction1D-[Warning] No sample set for instrument in workspace.
IFunction1D-[Warning] Can't calculate wavelength in IkedaCarpenter.
IFunction1D-[Warning] Default all wavelengths to one.
IFunction1D-[Warning] Solution is to load appropriate instrument into workspace.

I'll create a separate issue for this.

[TOFarmer]

I'm assuming you just want one of us to test this, but I won't merge it just in case you are after both of us.

[arm61]

I'm assuming you just want one of us to test this, but I won't merge it just in case you are after both of us.

Was just spreading the odds