doc: document HDD_LEAVE_SPACE_DEFAULT chunkserver config setting

 Thanks, Marcin Sulikowski.

Signed-off-by: Dmitry Smirnov <onlyjob@member.fsf.org>
doc: don't use word "metadata" in chunkserver config.

Signed-off-by: Dmitry Smirnov <onlyjob@member.fsf.org>
doc: correct MASTER_RECONNECTION_DELAY timeout

Signed-off-by: Dmitry Smirnov <onlyjob@member.fsf.org>
doc: correct MASTER port number

Signed-off-by: Dmitry Smirnov <onlyjob@member.fsf.org>