document dirperm1 fix for #783 in known issues

Since `dirperm1` requires a more recent aufs patch than many current OS release,
we cant remove #783 completely. This documents that docker will apply `dirperm1`
automatically for systems that support it

Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com>

docs/sources/reference/builder.md

@@ -280,8 +280,14 @@ The cache for `RUN` instructions can be invalidated by `ADD` instructions. See
 
 - [Issue 783](https://github.com/docker/docker/issues/783) is about file
   permissions problems that can occur when using the AUFS file system. You
-  might notice it during an attempt to `rm` a file, for example. The issue
-  describes a workaround.
+  might notice it during an attempt to `rm` a file, for example.
+
+  For systems that have recent aufs version (i.e., `dirperm1` mount option can
+  be set), docker will attempt to fix the issue automatically by mounting
+  the layers with `dirperm1` option. More details on `dirperm1` option can be
+  found at [`aufs` man page](http://aufs.sourceforge.net/aufs3/man.html)
+
+  If your system doesnt have support for `dirperm1`, the issue describes a workaround.
 
 ## CMD
 

docs/sources/release-notes.md

@@ -57,7 +57,14 @@ impact on users. This list will be updated as issues are resolved.
 * **Unexpected File Permissions in Containers**
 An idiosyncrasy in AUFS prevents permissions from propagating predictably
 between upper and lower layers. This can cause issues with accessing private
-keys, database instances, etc. For complete information and workarounds see
+keys, database instances, etc.
+
+For systems that have recent aufs version (i.e., `dirperm1` mount option can
+be set), docker will attempt to fix the issue automatically by mounting
+the layers with `dirperm1` option. More details on `dirperm1` option can be
+found at [`aufs` man page](http://aufs.sourceforge.net/aufs3/man.html)
+
+For complete information and workarounds see
 [Github Issue 783](https://github.com/docker/docker/issues/783).
 
 * **Docker Hub incompatible with Safari 8**