Action-792 (Add note in test case document that negative tests 'go down' and positive tests 'go up')

Dear All,

I added sentences in these 3 sections. Please take a look.

      [1] http://www.w3.org/2005/rules/wiki/Test#Positive_Syntax_Tests
      [2] http://www.w3.org/2005/rules/wiki/Test#Negative_Syntax_Tests
      [3] http://www.w3.org/2005/rules/wiki/Test#Semantic_Tests

The test metadata design is not finalized or agreed upon, but so far we have
said that the metadata will have a dialect element for each dialect that the
test applies to (i.e. people won't need to use the knowledge given in these
notes when selecting tests).

The document needs updating for Core and PRD and to cover import scenarios
in syntax tests, I can plan to do that.

Stella