Add recommendation note

Add note that it is not recommended to use --no-metadata because it may breaks
synchronisation between git and svn.

Author: nemoinho

book/09-git-and-other-scms/sections/import-svn.asc

@@ -32,6 +32,7 @@ Then, redirect that output into your `users.txt` file so you can add the equival
 
 You can provide this file to `git svn` to help it map the author data more accurately.
 You can also tell `git svn` not to include the metadata that Subversion normally imports, by passing `--no-metadata` to the `clone` or `init` command.
+However this is not recommended because it breaks the two-way synchronisation between the git repository and the svn repository.
 This makes your `import` command look like this:
 
 [source,console]