Fix broken links (#195)

* Add section Getting started

Provide reading lists of documentation resources as discussed in Medley issue 1131.

* Fix broken links

As per the discussion in PR 192.

* Fix broken link

Fix broken link LOOPS Documentation PDF.

Author: pamoroso

content/en/software/using-medley/_index.md

@@ -25,7 +25,7 @@ Most of these resources were created decades ago when Medley was a research syst
 
 #### Introductory material
 
-1. [The Basics of Interlisp](Using). Essential information on the Interlisp language and the differences with Common Lisp.
+1. [The Basics of Interlisp](/software/Using.html). Essential information on the Interlisp language and the differences with Common Lisp.
 1. [Medley for the Novice](https://interlisp.org/documentation/Medley-Primer.pdf) (also known as Medley Primer).  An introductory guide to the basics of Medley such as executing commands, using menus and files, manipulating windows, editing and saving Lisp code, using the development tools, and more. Read it in full. The code in chapter 20 "Free Menus" doesn't work and some illustrations are missing.
 1. [SEdit — The Lisp Editor](https://drive.google.com/file/d/12LW5zCZauJvC63NRMJhjNv5qJkuuCflb/view?usp=sharing). The manual of SEdit, the default Lisp code editor.
 1. [LispCourse notes](https://interlisp.org/pub-pdfs/lispcourse/lispcourse.pdf). The notes of a beginner course on the Interlisp environment that goes from the basics of interacting with the system to programming in Lisp. Highly recommended. Skip the sections on printing and the network as modern Medley doesn't fully implement the described functionality. The formatting of the text is partially broken and some sections are missing.
@@ -54,9 +54,9 @@ For the searcher's conveneience, these have also been combined into searchable P
 #### Exported Medley Documentation
 These documents were converted from Medley's internal format into PDFs. Watch out for weird formatting, but these are firsthand sources on Medley features and applications.
 
-- <a href="All-Medley-PDFs.pdf">Medley Internal Documentation PDF</a>
-- <a href="All-Notecards-PDFs.pdf">Notecards Documentation PDF</a>
-- <a href="All-LOOPS-PDFs.pdf">LOOPS Documentation PDF</a>
+- [Medley Internal Documentation PDF](https://interlisp.org/documentation/All-Medley-PDFs.pdf)
+- [Notecards Documentation PDF](https://interlisp.org/documentation/All-Notecards-PDFs.pdf)
+- [LOOPS Documentation PDF](https://interlisp.org/documentation/All-Loops-PDFs.pdf)
 
 
 ### Interlisp Books