Some links and typos

[Ivo-Balbaert]

Description

1. frontpage: tutorial link not found, should be: https://docs.clio-lang.org/learn/official-tutorial

2. https://docs.clio-lang.org/getting-started
   and run the automatically generated index.clio file with clio run index.clio ??

3. https://docs.clio-lang.org/learn/official-tutorial/introduction
   playground: make link
   idem on: https://docs.clio-lang.org/learn/official-tutorial/prepreparation

4. https://docs.clio-lang.org/learn/official-tutorial/calls
   run call <-- call

[codecov]

Codecov Report

Merging #210 (0137227) into develop (42b289a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #210   +/-   ##
========================================
  Coverage    86.23%   86.23%           
========================================
  Files           53       53           
  Lines         1489     1489           
  Branches       239      239           
========================================
  Hits          1284     1284           
  Misses         176      176           
  Partials        29       29           

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