What you need
An ISO of PAL Melee or NTSC Melee (v1.02). You must find your own ISO.
The community build patches (you only need one):
NTSC Patch Rest of the World
PAL Patch Europe/Australia
Patching your copy of Melee
Extract the file you've downloaded (MNCB v0.2.0 - PAL.rar or MNCB v0.2.0 - NTSC.rar). Open the Tools folder and open xdeltaUI.exe. On the Apply Patch tab you must click Open which is to the right of the first empty space. Once you've clicked it another window will show up. Go into the Patch folder and select the file which is inside it (MNCB_PAL_Patch_v2.xdelta or MNCB_PAL_Patch_v2.xdelta) and press Open. Once you've done this press Open which is to the right of the second empty space. Now you must select your melee ISO file and press Open. Make sure you're using the correct version of melee. Now press the button which is next to the third empty space. Select the folder where you'd like the new ISO file to be created and give it a file name (ex: community_melee.iso) and press Save. Now press the Patch button.
How to use this on Dolphin
Move the newly created file into the same folder where your ordinary melee ISO (and other Gamecube/Wii games) is located. Re-open Dolphin and you're set! Since the community build uses a different ID you do not have to mess around with cheat codes. Have fun!