settings: Add glob: as prefix for file globbing maps

This gives the advantage to differentiate internal options from user defined
file globs with the same name.

runtime/help/options.md

@@ -669,6 +669,21 @@ all files except Go files, and `tabsize` 4 for all files except Ruby files:
 
 Or similarly you can match with globs:
 
+```json
+{
+    "glob:*.go": {
+        "tabstospaces": false
+    },
+    "glob:*.rb": {
+        "tabsize": 2
+    },
+    "tabstospaces": true,
+    "tabsize": 4
+}
+```
+
+You can also omit the `glob:` prefix before globs:
+
 ```json
 {
     "*.go": {
@@ -681,3 +696,6 @@ Or similarly you can match with globs:
     "tabsize": 4
 }
 ```
+
+But it is generally more recommended to use the `glob:` prefix, as it avoids
+potential conflicts with option names.