updates ldap doc for centos #12447

docs/installation/6-ldap.md

@@ -15,7 +15,7 @@ sudo apt install -y libldap2-dev libsasl2-dev libssl-dev
 On CentOS:
 
 ```no-highlight
-sudo yum install -y openldap-devel
+sudo yum install -y openldap-devel python3-devel
 ```
 
 ### Install django-auth-ldap