Updated blueprints documentation page.

[Unisay]

Resolves IntersectMBO/plutus-private#1118

• [x] Add required pragmas.
• [x] Fix broken include of the plutus.json
• [x] Document HasBlueprintDefinition and HasBlueprintSchema type-classes.
• [x] Remove obsolete rtd tags -- BEGIN BLOCKX in favor of semantic tags, e.g. -- BEGIN write blueprint to file

[Unisay]

The documentation looks excellent, but I don't think you intended to create a top-level plutus.json, did you?

There is the plutus.json file in the root of the docusaurus project (doc/docusaurus). It doesn't work and at the moment the blueprint example which refers to the plutus.json is broken - (its some HTML markup that is rendered, not JSON).

I wanted to fix this error and after reading the corresponding docusaurus doc I moved it to the doc/docusaurus/static folder. This way plutus.json gets copied over to the build dir, and can be referred to from there.