My blog has moved and an updated version of this post is located here http://brockhatfield.com/flash-ddwrt-netgear-nighthawk-r7000/
Honestly the process of flashing the Netgear Nighthawk R7000 to DD-WRT is a really easy, straight forward process. Unfortunately it was difficult to find some place that states it plainly. So here it is. The firmware’s can be found here. http://desipro.de/ddwrt/K3-AC-Arm/ First you need to get a .chk file from the Initial folder found here http://desipro.de/ddwrt/K3-AC-Arm/Initial/. Make sure you’ve grabbed the correct firmware for your model of router. In this case you want the file dd-wrt.K3_R7000.chk That .chk file is an old version of the router firmware. You don’t want to be stuck with that. So you also need to grab the update file. The latest is 24500M but at the time of writing it was exhibiting some issues with the 5Ghz channels being visible/accessible. So far now you want to grab 24345M from here http://desipro.de/ddwrt/K3-AC-Arm/24345M/ You have two choices of firmware in this folder with bittorrent and without bittorrent client. Pick your poison. Flashing to the new firmware will wipe all of your settings! There is also always a slim risk you might void your warranty or brick your router. Not my problem. Now all you need to do is login to your router’s web interface at 192.168.1.1(provided you haven’t previously changed it).
Go to the “Advanced” tab. Click “Administration” from the left side menu. Choose “Firmware Update”. Click “choose file” Browse to and select the “dd-wrt.K3_R7000.chk” file. Click “Upload” I don’t have the firmware in front of me but I believe this kicks off the whole update. If you get any other prompts just follow the directions. You may also end up at a white screen. The firmware tries to return you to the Netgear firmware page which is no longer present on your router. After you get back to steady blinking lights on the router your upgrade is done. Refresh the page for 192.168.1.1 in your browser. 
You will now be presented with the initial DD-WRT page that asks you to pick a username and a password. Fill those fields in and hit the “change password” button. Now click the “Administration” tab. Click the “Firmware Upgrade” tab. Click “Choose File”. Navigate to where you saved the update file dd-wrt.v24-K3_AC_ARM_STD_NEWD.bin(or BT file if applicable). You should now be in the process of upgrading this older version of DD-WRT to the latest and greatest that works properly. You are now done. Simple and painless. Enjoy your new super powered and open source driven router!