synapse/docs
..
sphinx
ancient_architecture_notes.rst
architecture.rst
code_style.rst
media_repository.rst
README.rst
turn-howto.rst

All matrix-generic documentation now lives in its own project at

github.com/matrix-org/matrix-doc.git

Only Synapse implementation-specific documentation lives here now (together with some older stuff will be shortly migrated over to matrix-doc)