Clarify named permission sets in configuration.md (#2916)

Co-authored-by: Jo Franchetti <jofranchetti@gmail.com>

Author: dandv

runtime/fundamentals/configuration.md

@@ -527,11 +527,22 @@ import * as module_2 from "@example/my-package/module2";
 
 ## Permissions
 
-Deno 2.5+ supports storing permission sets in the config file.
+Deno 2.5+ supports storing
+[permission](/runtime/fundamentals/security/#permissions) sets in the config
+file.
 
 ### Named permissions
 
-Permissions can be defined in key value pairs under the `"permissions"` key:
+Permissions can be defined as key-value pairs under arbitrarily-named permission
+sets under the `"permissions"` key. Within each set,
+
+- the key is the name of a
+  [permission](/runtime/fundamentals/security/#permissions) that would follow
+  `--allow-` or `--deny-` in the CLI invocation (i.e. `read`, `write`, `net`,
+  `env`, `sys`, `run`, `ffi`, `import`)
+- the value is a boolean (`true` / `false` correspond to allow / deny), an array
+  of strings representing paths, domains etc., or an object with `allow`,
+  `deny`, and/or `ignore` boolean key-value pairs.
 
 ```jsonc
 {
@@ -547,7 +558,8 @@ Permissions can be defined in key value pairs under the `"permissions"` key:
 }
 ```
 
-Then used by specifying the `--permission-set=<name>` or `-P=<name>` flag:
+Permission sets can be used by specifying the `--permission-set=<name>` or
+`-P=<name>` flag:
 
 ```sh
 $ deno run -P=read-data main.ts