docs: resolve todos and incomplete sections and missing links (#1394)

Signed-off-by: anna-charlotte <charlotte.gerhaher@jina.ai>
Signed-off-by: Charlotte Gerhaher <charlotte.gerhaher@jina.ai>
Co-authored-by: samsja <55492238+samsja@users.noreply.github.com>

docs/user_guide/representing/array.md

@@ -111,7 +111,7 @@ BannerDoc(image='https://example.com/image2.png', title='Bye Bye World', descrip
 
 !!! note
     The syntax `DocList[BannerDoc]` might surprise you in this context.
-    It is actually at the heart of DocArray but we'll come back to it later LINK TO LATER and continue with this example for now.
+    It is actually at the heart of DocArray, but we'll come back to it [later](#doclistdoctype-syntax) and continue with this example for now.
 
 As we said earlier, `DocList` (or more generally `AnyDocArray`) extends the `BaseDoc` API at the array level.
 

docs/user_guide/representing/first_step.md

@@ -48,20 +48,10 @@ The [BaseDoc][docarray.base_doc.doc.BaseDoc] class inherits from Pydantic [BaseM
 all the features of `BaseModel` in your `Doc` class. `BaseDoc`:
 
 * Will perform data validation: `BaseDoc` will check that the data you pass to it is valid. If not, it will raise an 
-error. Data being "valid" is actually defined by the type used in the type hint itself, but we will come back to this concept later. (TODO add typing section)
+error. Data being "valid" is actually defined by the type used in the type hint itself, but we will come back to this concept [later](../../data_types/first_steps.md).
 * Can be configured using a nested `Config` class, see Pydantic [documentation](https://docs.pydantic.dev/usage/model_config/) for more detail on what kind of config Pydantic offers.
 * Can be used as a drop-in replacement for `BaseModel` in your code and is compatible with tools that use Pydantic, like [FastAPI]('https://fastapi.tiangolo.com/').
 
-### How is `BaseDoc` different to Pydantic's `BaseModel`? (INCOMPLETE)
-
-LINK TO THE VERSUS (not ready)
-
-[BaseDoc][docarray.base_doc.doc.BaseDoc] is not just a [BaseModel](https://docs.pydantic.dev/usage/models):
-
-* You can use it with DocArray [Typed](docarray.typing) that are oriented toward Multimodal (image, audio, etc) data and for 
-Machine Learning use case TODO link the type section. 
-* [BaseDoc][docarray.base_doc.doc.BaseDoc] has an `id` field (generated by default) to uniquely identify a Document.
-
 ## Representing multimodal and nested data
 
 Let's say you want to represent a YouTube video in your application, perhaps to build a search system for YouTube videos.