[doc] clarify absolute path format for unix URIs (#37913)

Closes #37913

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37913 from markdroth:uri_doc_fix 06c3372b14
PiperOrigin-RevId: 685900366

doc/naming.md

@@ -34,12 +34,12 @@ Most gRPC implementations support the following URI schemes:
     resolver does not support this, but the c-ares based resolver
     supports specifying this in the form "IP:port".)
 
-- `unix:path`, `unix://absolute_path` -- Unix domain sockets (Unix systems only)
+- `unix:path`, `unix:///absolute_path` -- Unix domain sockets (Unix systems only)
   - `path` indicates the location of the desired socket.
   - In the first form, the path may be relative or absolute; in the
-    second form, the path must be absolute (i.e., there will actually be
-    three slashes, two prior to the path and another to begin the
-    absolute path).
+    second form, the path must be absolute (i.e., the last of the three
+    slashes is actually part of the path, so the path part of the URI is
+    `/absolute_path`).
 
 - `unix-abstract:abstract_path` -- Unix domain socket in abstract namespace (Unix systems only)
   - `abstract_path` indicates a name in the abstract namespace.