document that the home directory should be in /home for linux builds

Otherwise, it does not get automatically mounted in the schroot.
Recommend using a VM in case of such a scenario. Closes #1804.

INSTALL.md

@@ -28,7 +28,10 @@ Linux
 Please ensure that the cloned repository is in the user's home directory
 e.g. `~/wkhtmltopdf`. If you clone it in a different directory, it may
 fail with `E: Failed to change to directory /your/dir: No such file or directory`.
-Please note that [encrypted home directories are not supported](https://bugs.launchpad.net/ubuntu/+source/schroot/+bug/791908).
+Please note that [encrypted home directories](https://bugs.launchpad.net/ubuntu/+source/schroot/+bug/791908)
+and [non standard home directories](https://github.com/wkhtmltopdf/wkhtmltopdf/issues/1804)
+(i.e. not located in `/home`) are not supported -- you are advised to
+use a VM instead to build wkhtmltopdf.
 
 Building is supported only on the latest stable Debian/Ubuntu releases, and
 the binaries are produced in a self-contained chroot environment for the