Merge pull request #1482 from Autodesk/sabrih/add_instruction_devtool…

…set-6

Added instruction for installing devtoolset-6 on CentOS.

doc/build.md

@@ -235,7 +235,26 @@ To allow your tests to run, you can inject LD_LIBRARY_PATH into any of the mayaU
 
 There is a related ADDITIONAL_PXR_PLUGINPATH_NAME cmake var which can be used if schemas are installed in a non-standard location
 
+##### Devtoolset-6:
 
+Devtoolset-6, which includes GCC 6 on CentOS has been retired from the main repo and moved into the vault. Follow instructions below for installing devtoolset-6 on CentOS:
+
+```
+# download the packages, install may fail with "no public key found"
+sudo yum-config-manager --add-repo=http://vault.centos.org/7.6.1810/sclo/x86_64/rh/
+
+# to fix "no public key found"
+cd /etc/pki/rpm-gpg
+ls # confirm RPM-GPG-KEY-CentOS-SIG-SCLo exists
+sudo rpm --import RPM-GPG-KEY-CentOS-SIG-SCLo
+rpm -qa gpg* # confirm key with substring f2ee9d55 exists
+
+# to install devtoolset-6
+sudo yum install devtoolset-6
+
+# disable the vault after successful install
+sudo yum-config-manager --disable vault.centos.org_7.6.1810_sclo_x86_64_rh_
+```
 
 # How to Load Plug-ins in Maya