docs: change section title to filtering

Source code: :func:`sbws.lib.v3bwfile.V3BWFile.from_results`

Selecting bandwidth measurements

:::::::::::::::::::::::::::::::::::

Filtering the bandwidth measurements

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Each relay bandwidth measurements are selected in the following way:

1. At least two bandwidth measurements (``Result`` s) MUST have been obtained

#. At least two bandwidth measurements (``Result`` s) MUST have been obtained

   within an arbitrary number of seconds (currently one day).

   If they are not, the relay MUST NOT be included in the Bandwith File.

2. The measurements than are are older than an arbitrary number of senconds

#. The measurements than are are older than an arbitrary number of senconds

   in the past MUST be discarded.

   Currently this number is the same as ``data_period`` (5 days).