Added helpful strings

-Added a few helpful strings (more coming)
-Added welcome_msgs & conclusion_msgs function. We all would like a
warm welcome (but I’ll try to make it non-intrusive)
-Edited & corrected already existing strings
-Minor code adjustments
More helpful strings

-Added more helpful strings
-Script now doesn’t interrupt if no connection is found and no SDL
folder is found (in case someone wants only to install the support
libraries)
-Added interruption when nothing is found to install (only happens when
there is no internet
-Minor code adjustments