Text for CBC mchirp binned probabilities

See https://git.ligo.org/publications/o4/cbc/task_forces/-/issues/6 for more context.

The suggested text is along these lines :

The chirp mass of the source binary lies within the range (1.1, 1.2) Msun (probability 0.97).

These values will be extracted from the result of a 'CGMI' binned chirp mass calculation which provides arrays of N+1 bin edges and N probabilities. One algorithm for choosing the bin edges is the following :

1. Sort the bins in descending order of probability
2. Select bins in this order, stopping when the coverage is 90% or greater
3. Find the minimum lower and maximum upper edges of any selected bins, and add up the total probability between these edges. [Note that this may be larger than the coverage in step 2, in the rare corner case that the selected bins are non-contiguous.]
4. The total probability number should be rounded / presented in the same way as p_astro / p_embright probabilities.