Please add Syzygy to the list of external resources

[sebmarchand]

We have a lot of code to read and write PDBs in Syzygy: https://github.com/google/syzygy/tree/master/syzygy/pdb

See also our experimental pdb_dumper: https://github.com/google/syzygy/tree/master/syzygy/experimental/pdb_dumper