Don't mention unimplemented features in the documentation (#381)

Author: Luthaf

bindings/rascal/representations/spherical_covariants.py

@@ -32,8 +32,7 @@ class SphericalCovariants(BaseIO):
 
     gaussian_sigma_type : str
         How the Gaussian atom sigmas (smearing widths) are allowed to
-        vary -- fixed ('Constant'), by species ('PerSpecies'), or by
-        distance from the central atom ('Radial').
+        vary. Only fixed smearing width ('Constant') are implemented.
 
     gaussian_sigma_constant : float
         Specifies the atomic Gaussian widths, in the case where they're

bindings/rascal/representations/spherical_expansion.py

@@ -32,8 +32,7 @@ class SphericalExpansion(BaseIO):
 
     gaussian_sigma_type : str
         How the Gaussian atom sigmas (smearing widths) are allowed to
-        vary -- fixed ('Constant'), by species ('PerSpecies'), or by
-        distance from the central atom ('Radial').
+        vary. Only fixed smearing width ('Constant') are implemented.
 
     gaussian_sigma_constant : float
         Specifies the atomic Gaussian widths, in the case where they're

bindings/rascal/representations/spherical_invariants.py

@@ -48,8 +48,7 @@ class SphericalInvariants(BaseIO):
 
     gaussian_sigma_type : str
         How the Gaussian atom sigmas (smearing widths) are allowed to
-        vary -- fixed ('Constant'), by species ('PerSpecies'), or by
-        distance from the central atom ('Radial').
+        vary. Only fixed smearing width ('Constant') are implemented.
 
     gaussian_sigma_constant : float
         Specifies the atomic Gaussian widths, in the case where they're