First, look at /etc/openwrt_release (on your router). You will see a bunch of
attributes for the OpenWrt system. The DISTRIB_RELEASE attribute is your
OpenWrt version, and the first part of DISTRIB_TARGET (before the slash) is
the router's platform.

Now, open up /etc/opkg.conf (again, on your router) in your favourite editor.
Add a new line at the bottom, similar to this:
	src/gz bfgminer http://luke.dashjr.org/programs/bitcoin/files/bfgminer/latest/openwrt/15.05/ar71xx
In this example, 15.05 is the version of OpenWrt, and ar71xx is the platform.
Be sure to change those to match your router! You can also change "latest" to
"stable" or "testing" to get better-tested versions.

Next, save the file and exit your editor. Tell opkg to reload its package lists
by running the command:
	opkg update
If you get a "404 Not Found" error, then your router may not be supported. If
you open an issue for your router's platform, it may be possible to add
support.

If all went well updating your package list, you can now install BFGMiner and
any drivers you might need:
	opkg install bfgminer
	opkg install kmod-usb-serial-ftdi
	opkg install kmod-usb-serial-cp210x
	opkg install kmod-usb-serial-pl2303