docs: remove redundant retries from swig_doc.py

With proper build dependencies, it should not be needed.

volk: make sure the alignment call for a block passes at least 1.

For machines with an alignment of 1, the blocks were truncating the aligment to 0. This makes sure that it gets set to a minimum of 1.

docs: Adding gr-fft to sphinx docs

docs: Fixed copyright in sphinx docs.

docs: Extended README for sphinx docs.