Added basic docs on services

docs/docs/documentation/supplementary-services/annotations.md

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+description: Discover everything about the annotations service
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 # Annotations
+
+The `Annotations Service` is responsible to provide commenting capabilities and communication threads to users, that can be attached to any entity.
+
+Currenty, users can communicate in threads that attach to [description template](/docs/documentation/administration/templates/) questions. There is a `comments` button next to the titles of the questions, which brings up a modal with the threads attached to them when clicked. Here, users can either create new threads or respond to existing ones. Comments can also be flaged as `hidden` which makes them visible only to their authors. 
+
+All of this information is getting handled independently of the main platform, using this service.

docs/docs/documentation/supplementary-services/deposit-services.md

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+description: Discover everything about the deposit services
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 # Deposit Services
+
+The `Deposit Services` are independent third party services responsible to provide a place to store and validate data objects *(in our case [plans](/docs/documentation/application/plans/))*. They are used as a source of trust and provide a unique key / signature *(called **DOIs** or **D**ata **O**bject **I**dentifiers)* for every data entity deposited to them.
+
+This platform is directly integrated with the [Zenodo](https://zenodo.org/) deposit.

docs/docs/documentation/supplementary-services/file-transformers.md

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+description: Discover everything about the file transformer services
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 # File Transformers
+
+The `File Transformer Services` are standalone services responsible to provide a way for users to download [plans](/docs/documentation/application/plans/) and [descriptions](/docs/documentation/application/descriptions/) in various file formats. So, their role is to *"transform"* these data structures to these formats.
+
+There are currently two file transformer services implemented and integrated.
+
+- **Docx file transformer service**: Used for PDF files and Word documents.
+- **Rda file transformer service**: Used for JSON files following the RDA specification.

docs/docs/documentation/supplementary-services/notifications/index.md

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 # Notifications
 
+The `Notifications Service` is responsible to inform users about important events taking place in the platform that relate with them. The contents of these notifications can be [configured](/docs/documentation/administration/notification-templates) and they depend on the type of notification. By type, we mean the event that triggered them. For example, if a user gets invited to a [plan](/docs/documentation/application/plans/), this is considered an event and a notification gets pushed to the user it refers to.
+
+The notifications sent, can use one of the following available channels. They can either be `InApp` or `Email`. More detals about these notification channels can be found on the links below.
+
 import DocCardList from '@theme/DocCardList';
 
 <DocCardList />