Stereo node fix

[Erol444]

what else is missing in the docs @szabi-luxonis ?

[SzabolcsGergely]

Subpixel mode description should be changed, 3 is the default now instead 5.
https://github.com/luxonis/depthai-python/pull/428/files#diff-acfee2c382896d3423be1a43a5edd9e862b4083769fe1a59e8cfd4bc60bacdeaR122

instead this:

        then software interpolation is done on Shave, resulting a final disparity with 5 fractional bits, resulting in significantly more granular depth
        steps (32 additional steps between the integer-pixel depth steps), and also theoretically, longer-distance depth viewing - as the maximum depth
        is no longer limited by a feature being a full integer pixel-step apart, but rather 1/32 of a pixel. In this mode, stereo cameras perform: :code:`96 depth steps * 32 subpixel depth steps = 3,072 depth steps.`
        Note that Subpixel and Extended Disparity are not yet supported simultaneously (which would result in :code:`191 * 32 = 6,112 depth steps`), but should be available in the near future (`Pull Request <https://github.com/luxonis/depthai-python/pull/347>`__).

change to:

        then software interpolation is done on Shave, resulting a final disparity with 3 fractional bits, resulting in significantly more granular depth
        steps (8 additional steps between the integer-pixel depth steps), and also theoretically, longer-distance depth viewing - as the maximum depth
        is no longer limited by a feature being a full integer pixel-step apart, but rather 1/8 of a pixel. In this mode, stereo cameras perform: :code:`95 depth steps * 8 subpixel depth steps + 1 = 761 depth steps.`
        Note that Subpixel and Extended Disparity are not yet supported simultaneously.).