Add explainer about Spotlight indexing slowness

docs/FAQ.md

@@ -90,7 +90,9 @@ macOS doesn't allow direct downgrades, as such you will have to wipe the disk in
 
 ## Why is my system slow?
 
-This can mean many things. Firstly, newer operating systems are harder to run and can appear more slow.
+This can mean many things. Firstly, newer operating systems are harder to run and can appear more slow. 
+
+Additionally if your macOS installation is recent, Spotlight starts creating a full disk index which can cause high CPU load, high temps and general slowness. It's recommended to keep the system running for few hours, once Spotlight has indexed the load will ease. A way to check whether it's caused by Spotlight is to open Activity Monitor, choosing the "All Processes" from the "View" menu item to see if a process called ```mds_stores``` is using a lot of CPU resources.
 
 However, if your system is being **really** slow and you have no transparency in Dock and menubar, this typically indicates that root patches are not installed and as such there is no acceleration. Make sure to install root patches to get proper drivers and functionality. Refer to [Applying post install volume patches](https://dortania.github.io/OpenCore-Legacy-Patcher/POST-INSTALL.html#applying-post-install-volume-patches) and the [Troubleshooting](https://dortania.github.io/OpenCore-Legacy-Patcher/TROUBLESHOOTING.html) section for more information.