Add section with optional advanced configurations

doc/NR_SA_CN5G_gNB_USRP_COTS_UE_Tutorial.md

@@ -244,3 +244,9 @@ iperf -s -u -i 1 -B 12.1.1.2
 ```bash
 docker exec -it oai-ext-dn iperf -u -t 86400 -i 1 -fk -B 192.168.70.135 -b 100M -c 12.1.1.2
 ```
+
+# 6. Advanced configuration (optional)
+
+- If you get real-time problems on heavy UL traffic, reduce the maximum UL MCS using an additional command-line switch: `--MACRLCs.[0].ul_max_mcs 14`.
+
+- There is noise on the DC carriers on N300 and especially the X300 in UL. To avoid their use or shift them away from the center to use more UL spectrum, use the `--tune-offset <Hz>` command line switch, where `<Hz>` is ideally half the bandwidth, or possibly less.