fix URL formatting, add note on **api**.github.com certificates (#2886)
fix URL formatting, add note on **api**.github.com certificates (#2886)

* fix URL formatting, add note on private repos & certificates

* fix TLS / TSL typo

* clarify when api.github.com certificates are needed

according to https://github.com/larshp/abapGit/pull/2886#discussion_r316257182

larshp/abapGit,sbcgua/abapGit,EduardoCopat/abapGit,sbcgua/abapGit,larshp/abapGit,EduardoCopat/abapGit