add note on installing on mac silicon. see #198 for full conversation (…

…#222)

python/caches/README.md

@@ -16,6 +16,15 @@ $ python3 -m pip install --upgrade pip
 $ python3 -m pip install hydrotools.caches
 ```
 
+### Mac Silicon Note
+
+If you experience issues installing the `tables` library while installing
+`hydrotools.caches`, you likely need to install `HDF5` and/or set the `HDF5_DIR`
+environement variable prior to installation. Brew users should install
+`HDF5` using `brew install hdf5` and try reinstalling `hydrotools.caches` using
+`env HDF5_DIR=$(brew --prefix hdf5) pip install hydrotools.caches`. If you've 
+already installed `HDF5` via brew, ignore the first step.
+
 ## Usage
 
 The following example demonstrates how one might use `hydrotools.caches.hdf` to cache a `pandas.dataframe` generated by a long running process.