Add glossary to docs

This commit adds a glossary to the documentation, providing definitions for key
terms used in the Yorkie project and community. This addition will help users
better understand the terminology used in the project.

docs/glossary.mdx

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+---
+title: 'Glossary'
+order: 100
+---
+
+## Glossary
+
+This words are used in the Yorkie project and the community.
+
+| Word | Description |
+| ---- | ----------- |
+| Yorkie | An open-source document store for building real-time collaborative applications. Sometimes it refers to the [main repository](https://github.com/yorkie-team/yorkie). |
+| Client | An regular client that communicates with the Yorkie server, synchronizing document changes for real-time collaboration. |
+| Server | The central component that manages documents, stores changes, and facilitates communication between clients. |
+| Project | A logical grouping of documents and clients, allowing multiple independent services within a single Yorkie installation. |
+| Document | The primary data structure in Yorkie. It contains a presence and a root. |
+| Presence | A data structure representing a user's current state within a document (e.g., cursor position, selection). |
+| Root | The main JSON-like data structure(CRDT) within a document that can be shared and edited by multiple users. |
+| Change | A representation of modifications made to a document, created by calling `Document.Update()`. |
+| PushPullChanges | An API for bidirectional synchronization of changes between clients and the server. |
+| Checkpoint | A mechanism for tracking the synchronization state between clients and the server, consisting of ServerSeq and ClientSeq. |
+| Housekeeping | A maintenance process that cleans up unnecessary data on the server. |
+| CRDT Element | A data structure representing a CRDT element, analogous to an Element in the DOM. For more information, see [Data Structures](https://github.com/yorkie-team/yorkie/blob/main/design/data-structure.md). |
+| CRDT Node | A single node within a CRDT element. |
+| Tombstone | A marker for a deleted node or element in CRDT. |
+| Garbage Collection | The process of removing nodes marked as tombstones to optimize storage and performance. |
+
+<br/>
+
+> If you want to add a new word to the glossary, please create a pull request with the new word and its description.