Mention the --enable-symlinks option in INSTALL
Mention the --enable-symlinks option in INSTALL

From version 2.11 onwards, the default for Ganeti is to install as
a standby version to be activated by the old Ganeti version itself.
While this is useful for existing users, first-time installations
need to add these symlinks or configure with ``--enable-symlinks``.
Add this information to the INSTALL instructions.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>

mbakke/ganeti,andir/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,ganeti/ganeti,dimara/ganeti,mbakke/ganeti,andir/ganeti,ganeti/ganeti,onponomarev/ganeti,leshchevds/ganeti,yiannist/ganeti,mbakke/ganeti,andir/ganeti,leshchevds/ganeti,yiannist/ganeti,apyrgio/ganeti,ganeti/ganeti,dimara/ganeti,bitemyapp/ganeti,onponomarev/ganeti,apyrgio/ganeti,yiannist/ganeti,leshchevds/ganeti,bitemyapp/ganeti,ganeti-github-testing/ganeti-test-1