diff --git a/FAQ.md b/FAQ.md
index 1000ab1..da4887f 100644
--- a/FAQ.md
+++ b/FAQ.md
@@ -44,18 +44,36 @@ If you want the ccls binary at a specific location use a symlink - do not move t
 
 ### Project root detection
 
-For C++ projects, `compile_commands.json` is used by [emacs-ccls](https://github.com/MaskRay/emacs-cquery/) to mark the project root. This is usually a symlink to the real `compile_commands.json` in a build directory:
+[emacs-ccls](https://github.com/MaskRay/emacs-cquery/) locates the project root with `ccls-project-root-matchers`:
+
+* `.ccls-root`. If this file exists in any parent directory, that directory is treated as the project root.
+* `projectile-project-root`. Then this function is called. You likely don't want `/usr/include/c++/8/algorithm` to be treated as in the project `/usr/include/c++/8/`, `(setq projectile-require-project-root t)` inhibit the behavior.
+
+Then ccls will find `.ccls` or `compile_commands.json` in the root directory.
 
 ```
 proj
- build
-  gen
-    generated_file_in_build.cc
+  .ccls-root  # Use this file if you want subproject files to be associated with the root project
   compile_commands.json
- compile_commands.json -> build/compile_commands.json
+  subproj0
+    .git
+  subproj1
+    .git
 ```
 
-In this example, the `:rootUri` of the generated C++ file is `proj/build/` because of `proj/build/compile_commands.json`. However, the user wants it to be `proj/`. Customize `MaskRay-root-matchers`.
+### Maximum number of file descriptors
+
+When indexing ccls itself, some files require more than 1000 file descriptors. Remember to increase `RLIMIT_NOFILE`.
+
+```zsh
+ulimit -n 32768
+```
+
+`/etc/security/limits.conf`:
+```
+* hard  nofile    32768
+* soft  nofile    32768
+```
 
 ### Includes