Add documentation of `make update-checksum-*`

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Merge pull request #334 from TimothyGu/stable-s

Add documentation of `make update-checksum-*`
doc update: add legal notes

from a long time ago:
http://lists.nongnu.org/archive/html/mingw-cross-env-list/2011-03/msg00107.html
doc update: add GNU Licenses FAQ
Mention new member of core team: Timothy Gu
doc update: fix list nesting
package boost: disable icu
Add minimum RAM and disk requirements to website

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Lensfun has moved to sourceforge.net

The lensfun project has moved to sourceforge.net pending the close-down of
berlios.de by the end of April. This patch updates lensfun.mk accordingly.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Update lensfun's URL on website

Signed-off-by: Timothy Gu <timothygu99@gmail.com>