This allows correctly documenting dynamic enable conditions.
E.g:
```nix
enable = mkEnableTargetWith {
name = "QT";
autoEnable = pkgs.stdenv.hostPlatform.isLinux;
autoEnableExpr = "pkgs.stdenv.hostPlatform.isLinux";
};
```
`autoEnableExpr` will be wrapped in parentheses if it contains a nix
operator with lower precedence than `&&`.
Added a note in the docs mentioning `mkEnableTarget` should either have
a static `autoEnable` or specify `autoEnableExpr`.
0449dae6d4
