docs: rename display name to LocalThings

"Local Things" read as two separate words; the integration is one name,
LocalThings (as in local SmartThings control).

custom_components/localthings/manifest.json

@@ -1,6 +1,6 @@
 {
   "domain": "localthings",
-  "name": "Local Things",
+  "name": "LocalThings",
   "codeowners": ["@mbillow"],
   "config_flow": true,
   "dependencies": [],