clarify location of cloned repository for linux builds

In case the cloned repository is out of the home directory, starting
the schroot can fail with an error "Failed to change to directory".

INSTALL.md

@@ -23,8 +23,9 @@ CentOS 5       | ```sudo scripts/build.py setup-schroot-centos5```
 MinGW-w64      | ```sudo scripts/build.py setup-mingw-w64```
 
 Please note that you should run the above commands while logged in as a
-regular user who has ```sudo``` access. **Do not attempt to clone the
-repository or run any other command as root!**
+regular user who has ```sudo``` access and that the cloned respository
+should be in the user's home directory e.g. ```~/wkhtmltopdf```. **Do
+not attempt to clone the repository or run any other command as root!**
 
 The MinGW-w64 toolchain can cross-compile 32/64-bit Windows binaries from
 Linux -- it is useful for targetting Windows XP/Windows 2003, which are not