Okay, so I fixed it.
Put the tags in the header as usual, then upload the smallest (16x16 as ico) to the general section. This will be the one that nodebb overrides the others with.
The others will still work for other systems like android and such.
Well... If you already have NodeBB running on port 80 without nginx/Apache proxy, then you can not assign another service on the port as well. I recommend you to set up an nginx/Apache proxy for NodeBB and create virutal hosts for each service you want to run on port 80 (this way you can run multiple services/sites on port 80).
@abhinov-singh With a normal configuration, NodeBB needs MongoDB running. You can check it with:
service mongod status
Also, you can try from your nodebb folder:
See also your nodebb/logs/output.log file, or just the recent lines with:
(Ctrl-C to exit)