File README.SUSE.packaging of Package maxima

Note to packagers:
* The availability of multiple providers of maxima_exec (namely,
  maxima-exec-clisp and maxima-exec-sbcl) will affect the build dependencies
  (but not the runtime deps) of any package depending on maxima, leaving the
  package in an `unresolvable` state. This should be fixed at the affected
  package's specfile with an additional `BuildRequires: maxima-exec-${flavor}`.
  See for example, how this is done for wxMaxima (obs://Education/wxMaxima). 
* When building multiple lisp flavours, maxima sets `sbcl` as the preferred
  default lisp but it tries and finds other lisp implementations just fine in
  case `maxima-exec-sbcl` is not installed. Thus, one only needs the weaker
  `Suggests` on `maxima-exec-sbcl` for `maxima` rather than a `Requires` or
  even `Recommends`.
* At least one `maxima-exec-${flavor}` must be installed for `maxima` to work;
  this is ensured by the `Requires: maxima_exec` for `maxima`.