Tutorials: add link for Ettus UHD installation page and remove 'source oaienv' from instructions

doc/NR_SA_Tutorial_COTS_UE.md

@@ -58,6 +58,7 @@ sudo ./program_uicc --adm 12345678 --imsi 001010000000001 --isdn 00000001 --acc
 
 ### Build UHD from source
 ```bash
+# https://files.ettus.com/manual/page_build_guide.html
 sudo apt install -y autoconf automake build-essential ccache cmake cpufrequtils doxygen ethtool g++ git inetutils-tools libboost-all-dev libncurses5 libncurses5-dev libusb-1.0-0 libusb-1.0-0-dev libusb-dev python3-dev python3-mako python3-numpy python3-requests python3-scipy python3-setuptools python3-ruamel.yaml
 
 git clone https://github.com/EttusResearch/uhd.git ~/uhd
@@ -87,9 +88,7 @@ cd ~/openairinterface5g/cmake_targets
 ./build_oai -I
 
 # Build OAI gNB
-cd ~/openairinterface5g
-source oaienv
-cd cmake_targets
+cd ~/openairinterface5g/cmake_targets
 ./build_oai -w USRP --ninja --gNB -C
 ```
 
@@ -106,24 +105,18 @@ docker compose up -d
 
 ### USRP B210
 ```bash
-cd ~/openairinterface5g
-source oaienv
-cd cmake_targets/ran_build/build
+cd ~/openairinterface5g/cmake_targets/ran_build/build
 sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.fr1.106PRB.usrpb210.conf --sa -E --continuous-tx
 ```
 ### USRP N300
 ```bash
-cd ~/openairinterface5g
-source oaienv
-cd cmake_targets/ran_build/build
+cd ~/openairinterface5g/cmake_targets/ran_build/build
 sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band77.fr1.273PRB.2x2.usrpn300.conf --sa --usrp-tx-thread-config 1
 ```
 
 ### USRP X300
 ```bash
-cd ~/openairinterface5g
-source oaienv
-cd cmake_targets/ran_build/build
+cd ~/openairinterface5g/cmake_targets/ran_build/build
 sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band77.fr1.273PRB.2x2.usrpn300.conf --sa --usrp-tx-thread-config 1 -E --continuous-tx
 ```