Add v2.7 sourcecode and licenses

Merge branch 'image_v2.6.2' for final release

Remove pynq from requirements.txt (Xilinx#1168)

Co-authored-by: Cathal McCabe <[email protected]>

Merge branch 'image_v2.6.0'

v2.5.1 updates to changelog (Xilinx#1015)

Update README.md and changelog for v2.5 (Xilinx#959)

Add register map text to the overlay tutorial (Xilinx#821)

Minor formatting fixes (Xilinx#733)

Update getting started video links

Update pynq_sd_card.rst

Looks to me the path was incorrect