Fix: incorrect urcu git URL in README

Reported-by: Ruslan Uvashev <ruslan.uvashev@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fix: mismatch between code and comments

Signed-off-by: Zifei Tong <zifeitong@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>