docs: fix typo for "category" in usage.md (#760)

Author: pinheadtf2

docs/usage.md

@@ -37,7 +37,7 @@ Create a new tag by accessing the "New Tag" option from the Edit menu or by pres
     -   Parent tags with the disambiguation check next to them will be used to help disambiguate tag names that may not be unique.
     -   For example: If you had a tag for "Freddy Fazbear", you might add "Five Nights at Freddy's" as one of the parent tags. If the disambiguation box is checked next to "Five Nights at Freddy's" parent tag, then the tag "Freddy Fazbear" will display as "Freddy Fazbear (Five Nights at Freddy's)". Furthermore, if the "Five Nights at Freddy's" tag has a shorthand like "FNAF", then the "Freddy Fazbear" tag will display as "Freddy Fazbear (FNAF)".
 -   The **color** option lets you select an optional color palette to use for your tag.
--   The **"Is Cagegory"** property lets you treat this tag as a category under which itself and any child tags inheriting from it will be sorted by inside the preview panel.
+-   The **"Is Category"** property lets you treat this tag as a category under which itself and any child tags inheriting from it will be sorted by inside the preview panel.
 
 ## Editing Tags