Documentation: add FAQ entry about clang not found

diff --git a/docs/admin/Faq.md b/docs/admin/Faq.md
index 2e5a7c4334fb6e30a125af3659a63915788adeea..d618d2b5705edb865bde690c6cb9a3f0d231040d 100644 (file)
--- a/docs/admin/Faq.md
+++ b/docs/admin/Faq.md
@@ -68,7 +68,7 @@ server development libraries (`postgresql-server-dev-9.5` on Ubuntu)
 and recompile (`cmake .. && make`).
 
 
-## I see the error "ERROR: permission denied for language c"
+### I see the error "ERROR: permission denied for language c"
 
 `nominatim.so`, written in C, is required to be installed on the database
 server. Some managed database (cloud) services like Amazon RDS do not allow
@@ -91,6 +91,11 @@ If you are using a flatnode file, then it may also be that the underlying
 filesystem does not fully support 'mmap'. A notable candidate is virtualbox's
 vboxfs.
 
+### I see the error: "clang: Command not found" on CentOS
+
+On CentOS 7 users reported `/opt/rh/llvm-toolset-7/root/usr/bin/clang: Command not found`.
+Double-check clang is installed. Instead of `make` try running `make CLANG=true`.
+
 ### nominatim UPDATE failed: ERROR: buffer 179261 is not owned by resource owner Portal
 
 Several users [reported this](https://github.com/openstreetmap/Nominatim/issues/1168) during the initial import of the database. It's