doc: add documentation on how to add TCs in the Test Suite

See merge request !119

and raises this error during the execution of the tests :

Multiple keywords with name 'Parse Ngsild Date' found. Give the full name of the keyword you want to use:
    assertionUtils.Parse Ngsild Date
    dateTimeUtils.Parse Ngsild Date

fix: incorrect temporal fragments representations

See merge request !118

fix: 1st round of fixes for CSR Test Cases

See merge request !117