Merge pull request #13 from molssi-seamm/kmesh

Added 1/length for k-grid spacing.

seamm_widgets/__init__.py

@@ -38,6 +38,7 @@
     "[length]": ["Å", "pm", "nm", "um"],
     "[length] ** 2": ["Å**2", "pm**2", "nm**2", "um**2"],
     "[length] ** 3": ["Å**3", "pm**3", "nm**3", "um**3"],
+    "1 / [length]": ["1/Å", "1/pm", "1/nm", "1/um"],
     "[mass]": ["g", "kg", "tonne", "lb", "ton"],
     "[substance]": ["mol"],
     "[temperature]": ["K", "degC", "degF", "degR"],