add note about chrooting

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

README.md

@@ -35,6 +35,8 @@ appreciated 💕 https://liberapay.com/grufwub/
 - Chroot and privilege dropping support (for now, Gophi compilation is
   reliant on a version of Go that has latest POSIX syscall fixes cherry
   picked, e.g. [my fork](https://github.com/grufwub/go/tree/go1.15.5-posix-syscall-fix))
+  NOTE: if you use a chroot and want to execute CGI scripts, you'll need
+  to set it up accordingly (symlink appropriate virtual filesystems)
 
 - Only 1 external dependency, `go-toml` brought in by my own `go-config`
   library