[Build] Add requirements.txt

ComfyUI discovers plugins from a `custom_nodes` directory, and so it
doesn't use the Python environment to locate plugins. However, we have
dependencies that must be installed into the Python environment for our
plugin to work.

It is implied in the docs that bundling a `requirements.txt` file is how
the ComfyUI CLI and Manager discovers and installs plugin dependencies.
In addition, a separate `requirements.txt` allows cleaner manual
installation (i.e. clone the repo under `ComfyUI/custom_nodes` then
`pip install -r requirements.txt`)

Signed-off-by: David Feltell <[email protected]>

Author: feltech

requirements.txt

@@ -0,0 +1,2 @@
+ openassetio>=1.0.0
+ openassetio-mediacreation>=1.0.0a12