Improve documentation

[felipesabino]

• Add JSDoc's documentation to each decorator function and its option object
  • @UnionType
  • @InterfaceType
  • @EnumType + @Value
  • @Field + @Arg + @OrderBy
  • @ObjectType
  • @InputObjectType
  • @Query
  • @Mutation
  • @Subscription
  • @Schema
  • @Before
  • @Root
  • @UseContainer
  • @After
• Improve README documentation
  • Explain each decorator. 💡 Create a Decorator reference similar to https://github.com/pleerock/routing-controllers#decorators-reference (tests are a good reference to the decorators usage example, specially the schema-factory specs)
  • Add examples for newly added decorators that differ from original fork
• ❓ separate each decorator example and doc into its own file inside docs/ folder
• Add a link reference to each example folder
• Add a CHANGELOG.md file, instead of having release notes on the Releases tab
• move CHANGELOG.md from docs folder to root

you can do it label

Instead of tacking all at decorators at once, which is just too huge and demanding, you can do several stuff just for one decorator, some options are:

• You can pick one of the new ones (located at the top of the readme) and add its documentation in the current README style, that would already help a lot
• You could just add some JSDoc documentation to the one of the decorators at src/decorator.ts or at their options object interface properties

[babbarankit]

I suggest we can place the differences with graphql-decorator at the bottom instead of the top of Project Page.
If need be we can give a link at top to see below for differences with the package.
If you agree, I will summit a PR!
Will also try to work on other thing mentioned above.