Add advice for avoiding the unable to open shared memory object error

Closes #158

Author: JackKelly

README.md

@@ -42,6 +42,8 @@ sudo apt install libgl1-mesa-glx  # For optical flow
 
 A (probably older) version is also available through `pip install nowcasting-dataset`
 
+To prevent PyTorch failing with an error like `RuntimeError: unable to open shared memory object </torch_2276740_2849291446> in read-write mode`, edit `/etc/security/limits.conf` as root and add this line: `*		 soft	 nofile		 512000` then log out and log back in again  (see [this issue](https://github.com/openclimatefix/nowcasting_dataset/issues/158) for more details).
+
 ## pip
 You can install a local version with `pip install -e .`.
 If you want to also install [PVLive](https://github.com/SheffieldSolar/PV_Live-API) then use `pip install git+https://github.com/SheffieldSolar/PV_Live-API