15 router manuals added

15 more router, modem, extender, and hotspot manuals were added recently:

- Belkin: 4 user manuals, 1 installation guide
- Huawei: 1 training guide
- Linksys: 1 user manual
- Motorola: 1 user manual
- Netgear: 2 user manuals, 3 setup manuals
- Verizon: 2 user manuals