Note about how to create custom xattr

I'm not sure if this is quite the whole truth of it, but a note like this would've helped me avoid some confusion.

On Ubuntu 20.1 with EXT4, this differs from the `attr` command, which automatically prefixes the key with `user.`.  So, if I add an xattr with the linux command `-s "testkey" "value" /path/to/file', I have to read from xattr with the key `user.testkey`.

1 files changed, 2 insertions, 0 deletions

diff --git a/README.rst b/README.rst
index c2c9214..24ccbd7 100644
--- a/README.rst
+++ b/README.rst
@@ -12,3 +12,5 @@ file system objects (files, directories, symlinks, etc).
 
 Extended attributes are currently only available on Darwin 8.0+ (Mac OS X 10.4)
 and Linux 2.6+. Experimental support is included for Solaris and FreeBSD.
+
+Note: custom xattr keys need to be prefixed with `user.`, ie: `user.your_attr`.