Change badge links in README to erf-model

[rafmudaf]

This pull request fixes a bug in the README where the CI status badges were pointing to the wrong repository. They now point to erf-model/ERF. Note that I've changed two links here: one for regression tests and one for unit tests. However, only one badge is displayed in the README. This structure was in anticipation of reporting CI status for the two levels of tests individually.

See #104.

[codecov-commenter]

Codecov Report

Merging #111 (e370565) into development (8bc67d9) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development     #111   +/-   ##
============================================
  Coverage        36.26%   36.26%           
============================================
  Files               41       41           
  Lines             2942     2942           
  Branches          1070     1070           
============================================
  Hits              1067     1067           
  Misses            1329     1329           
  Partials           546      546           

Flag	Coverage Δ
regtests	36.26% <ø> (ø)

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