Update tb-manual.torproject.org and git.torproject.org onion service link to v3 in README.md

As v2 onions are being removed, we need to update the site onion service in README.md file:

tb-manual

http://dgvdmophvhunawds.onion/ ->
http://dsbqrprgkqqifztta6h3w7i2htjhnq7d3qkh3c7gvc35e66rrcv66did.onion/

git.torproject.org

http://dccbbv6cooddgcrq.onion/ ->
http://xtlfhaspqtkeeqxk6umggfbr3gyfznvf4jhrge2fujz53433i2fcs3id.onion/

gitweb.torproject.org

http://jqs44zhtxl2uo6gk.onion/
http://gzgme7ov25seqjbphab4fkcph3jkobfwwpivt5kzbv3kqx2y2qttl4yd.onion/