Added notice about sudo -E

user-doc/Installation.txt

@@ -296,6 +296,9 @@ Then the PLUMED_PREFIX will be set equal to $HOME/opt.
 If the PLUMED_PREFIX is not set, it defaults to /usr/local.
 The install command should be executed with root permissions (e.g. "sudo make install")
 if you want to install PLUMED on a system directory.
+Notice that upon installation PLUMED currently needs to relink a library. If
+root user does not have access to compilers, "sudo -E make install" might solve
+the issue.
 An almost full copy of the compilation directory will
 be installed into $PLUMED_PREFIX/lib/plumed/ directory. A link to the proper
 PLUMED executable will be set up in $PLUMED_PREFIX/bin,