Update the JSON reporter docs for Suite.path.

doc/json_reporter.md

 JSON Reporter Protocol
 ======================
 
 The test runner supports a JSON reporter which provides a machine-readable
 representation of the test runner's progress. This reporter is intended for use
 by IDEs and other tools to present a custom view of the test runner's operation
 without needing to parse output intended for humans.
 
 Note that the test runner is highly asynchronous, and users of this protocol
 shouldn't make assumptions about the ordering of events beyond what's explicitly
@@ skipping 304 matching lines @@
   String path;
 }
 ```
 
 A test suite corresponding to a loaded test file. The suite's ID is unique in
 the context of this test run. It's used elsewhere in the protocol to refer to
 this suite without including its full representation.
 
 A suite's platform is one of the platforms that can be passed to the
 `--platform` option, or `null` if there is no platform (for example if the file
-doesn't exist at all). Its path is relative to the root of the current package.
+doesn't exist at all). Its path is either absolute or relative to the root of
+the current package.
 
 Suites don't include their own metadata. Instead, that metadata is present on
 the root-level group.
 
 ### Group
 
 ```
 class Group {
   // An opaque ID for the group.
   int id;
@@ skipping 28 matching lines @@
 class Metadata {
   // Whether the test case will be skipped by the test runner.
   bool skip;
 
   // The reason the test case is skipped, if the user provided it.
   String? skipReason;
 }
 ```
 
 The metadata attached to a test by a user.