Drop the enable_mps step from the Metal installation instructions

docs/getting_started/install.md

@@ -135,23 +135,8 @@ pip install "abtem[mps]"
 
 The extra is restricted to macOS on Apple silicon, since Metal exists nowhere else.
 
-To enable the backend, set `enable_mps` **before** *ab*TEM is imported — either through the environment:
-
-```{code-block}
-ABTEM_ENABLE_MPS=true python your_script.py
-```
-
-or in `~/.config/abtem/abtem.yaml`:
-
-```{code-block}
-enable_mps: true
-```
-
-```{note}
-`abtem.config.set(enable_mps=True)` does **not** work: the setting decides whether PyTorch is imported before
-FFTW, and by the time the call runs that has already been settled. PyTorch and FFTW each bundle their own copy
-of `libomp`, and a process that loaded FFTW's first crashes inside ordinary PyTorch operations.
-```
+Nothing needs enabling: *ab*TEM imports PyTorch the first time the `mps` device is used, so importing *ab*TEM
+stays as fast as without it.
 
 You can verify that Metal support is available using the code below:
 
@@ -171,6 +156,18 @@ potential = abtem.Potential(atoms, gpts=512, device="mps")
 probe = abtem.Probe(energy=200e3, semiangle_cutoff=20, device="mps")
 ```
 
+or make Metal the default device, with `abtem.config.set({"device": "mps"})` or in `~/.config/abtem/abtem.yaml`:
+
+```{code-block}
+device: mps
+```
+
+```{note}
+Import *ab*TEM (or PyTorch) before importing `pyfftw` yourself. PyTorch and FFTW each bundle their own copy of
+`libomp`, and PyTorch's has to be loaded first; *ab*TEM arranges that when it is imported. If `pyfftw` was
+imported earlier, using the `mps` device raises an error explaining this, rather than letting PyTorch crash.
+```
+
 Two things are worth knowing before you benchmark:
 
 - **Metal is single precision.** `precision` must be `float32`; pairing `device="mps"` with `float64` is