docs: add fastcore descriptions

README.md

@@ -19,6 +19,7 @@ NAVis is on [ReadTheDocs](http://navis.readthedocs.io/ "NAVis ReadTheDocs").
 * **render**: use Blender 3D for high quality [visualizations](https://youtu.be/wl3sFG7WQJc)
 * **R** neuron libraries: interfaces with [nat](https://github.com/jefferis/nat), [rcatmaid](https://github.com/jefferis/rcatmaid), [elmr](https://github.com/jefferis/elmr) and more
 * **import-export**: read/write SWCs, neuroglancer's ["*precomputed*"](https://github.com/google/neuroglancer/tree/master/src/datasource/precomputed) format, NMX/NML, NRRD, mesh-files and more
+* **fast**: uses functions compiled in Rust under-the-hood (see [fastcore](https://github.com/schlegelp/fastcore-rs))
 * **scalable**: out-of-the-box support for multiprocessing
 * **extensible**: build your own package on top of navis - see [pymaid](https://pymaid.readthedocs.io/en/latest/) for example
 

docs/source/install.rst

@@ -3,7 +3,7 @@
 Install
 =======
 
-NAVis currently requires Python 3.8 or later. Below instructions assume that
+NAVis currently requires Python 3.9 or later. Below instructions assume that
 you have already installed Python and its package manager ``pip``.
 
 .. topic:: By the way
@@ -67,6 +67,19 @@ These extras can be installed directly, or along with navis with
 The user-facing extras, the dependencies they install,
 and how to install those dependencies directly, are below.
 
+.. _fastcore:
+
+``fastcore``: `navis-fastcore <https://github.com/schlegelp/fastcore-rs>`_
+  ``navis-fastcore`` re-implements a bunch of low-level functions in Rust
+  and wraps them in Python. ``navis`` will use ``fastcore`` under-the-hood
+  if it is available. This is a highly recommended extra as it will
+  speed up certain operations such as geodesic distances, Strahler Index
+  or pruning by several orders of magnitude.
+
+  ::
+
+    pip3 install navis-fastcore
+
 
 .. _pykd: