Thanks to everyone that posted. It's been 10 months since I made this thread.
In case anyone else arrives here because they themselves are asking the same question, "how can I gently start getting back into jogging/running", I thought I'd share my experience.
I gave up on the idea of jogging or running, and instead focused on gentle resistance training at the gym, I started out doing around 20 minutes of gentle training. I can now do 1h 20mins, including a 1km brisk treadmill walk (6kmph) warm up on the treadmill. I don't suffer from PEM after doing this.
I'm not in remission, a month ago, I went for a swim after an absense of > 12 months (I used to swim regularly). I couldn't help myself and did 50 meters of butterfly stroke. I find that it's a 'fun' stroke to do, however it's very much an anaerobic excercise. That triggered PEM, and was a stern reminder that anaerobic excercise is a strong trigger of PEM.
I'm positive that there are a lot of different levels of illness in ME/CFS, for which I'm blessed to be fortunate enough to be able to do this type of moderate excercise. I'm not suggesting that it's for everyone, but if you're a mild case and are looking to excercise, I hope that you take it easy. The hardest thing about dragging myself to the gym hasn't been the excercise, it's been slowing myself down, and taking it easy.
Better to do 10 more moderate reps, than 10 strenuous ones for example. Taking big breaks between sets, letting the metabolic pathways recharge properly. Not getting a sweat on, monitoring the heart-rate for signs of over-exertion. It all works, and I've gained muscle mass. the excercise has also helped with various gut issues and digestion.
Thanks for the advice, I appreciated it all. That Mark VanNess video is top notch.