rest-api-changes.txt: Move documentation of magic paths to #file-id

The magic path names `/COMMIT_MSG` and `/MERGE_LIST` can be given
as input to multiple REST endpoints as the `file-id`.

Move the descriptions of those names from the List Files endpoint to
the file-id entity.

Bug: Issue 5855
Change-Id: I6ce3f909f27c51d149afd460b8e16dc9aef5dd34
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index b525826..69afaa5 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -4264,24 +4264,12 @@
 
 Lists the files that were modified, added or deleted in a revision.
 
-In addition the following magic files are included:
-
-* `/COMMIT_MSG`:
-+
-The commit message and headers with the parent commit(s), the author
-information and the committer information.
-
-* `/MERGE_LIST` (for merge commits only):
-+
-The list of commits that are being integrated into the destination
-branch by submitting the merge commit.
-
 .Request
 ----
   GET /changes/myProject~master~I8473b95934b5732ac55d26311a706c9c2bde9940/revisions/674ac754f91e64a0efb8087e59a176484bd534d1/files/ HTTP/1.0
 ----
 
-As result a map is returned that maps the file path to a list of
+As result a map is returned that maps the link:#file-id[file path] to a list of
 link:#file-info[FileInfo] entries. The entries in the map are
 sorted by file path.
 
@@ -4926,6 +4914,18 @@
 === \{file-id\}
 The path of the file.
 
+The following magic paths are supported:
+
+* `/COMMIT_MSG`:
++
+The commit message and headers with the parent commit(s), the author
+information and the committer information.
+
+* `/MERGE_LIST` (for merge commits only):
++
+The list of commits that are being integrated into the destination
+branch by submitting the merge commit.
+
 [[fix-id]]
 === \{fix-id\}
 UUID of a suggested fix.