consider removing "location of" options for crypto backends

[pabuhler]

This was suggest in PR #574 by @traud .

What about removing both ‘Location of’? They are auto-detected and required only if not the system provided library should be used. Actually, the switch for OpenSSL does not work for a current version of OpenSSL, when its was build in its source tree (there is no folder called /lib). Did not test NSS.

[traud]

One additionally note: Not removing it in general, just removing it in the Read Me – to make the Read Me easier to read.