Update various docs (#4)

* rename cli tool

* remove redundant docs

* update docs

* update macos instructions

* add badges

docs/development/contributing.md

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+# Package overview
+
+`kotaemon` library focuses on the AI building blocks to implement a RAG-based QA application. It consists of base interfaces, core components and a list of utilities:
+
+- Base interfaces: `kotaemon` defines the base interface of a component in a pipeline. A pipeline is also a component. By clearly define this interface, a pipeline of steps can be easily constructed and orchestrated.
+- Core components: `kotaemon` implements (or wraps 3rd-party libraries
+  like Langchain, llama-index,... when possible) commonly used components in
+  kotaemon use cases. Some of these components are: LLM, vector store,
+  document store, retriever... For a detailed list and description of these
+  components, please refer to the [API Reference](/reference/nav/) section.
+- List of utilities: `kotaemon` provides utilities and tools that are
+  usually needed in client project. For example, it provides a prompt
+  engineering UI for AI developers in a project to quickly create a prompt
+  engineering tool for DMs and QALs. It also provides a command to quickly spin
+  up a project code base. For a full list and description of these utilities,
+  please refer to the [Utilities](/development/utilities) section.
+
+```mermaid
+mindmap
+  root((kotaemon))
+    Base Interfaces
+      Document
+      LLMInterface
+      RetrievedDocument
+      BaseEmbeddings
+      BaseChat
+      BaseCompletion
+      ...
+    Core Components
+      LLMs
+        AzureOpenAI
+        OpenAI
+      Embeddings
+        AzureOpenAI
+        OpenAI
+        HuggingFaceEmbedding
+      VectorStore
+        InMemoryVectorstore
+        ChromaVectorstore
+      Agent
+      Tool
+      DocumentStore
+      ...
+    Utilities
+      Scaffold project
+      PromptUI
+      Documentation Support
+```
+
+# Common conventions
+
+- PR title: One-line description (example: Feat: Declare BaseComponent and decide LLM call interface).
+- [Encouraged] Provide a quick description in the PR, so that:
+  - Reviewers can quickly understand the direction of the PR.
+  - It will be included in the commit message when the PR is merged.
+
+# Environment caching on PR
+
+- To speed up CI, environments are cached based on the version specified in `__init__.py`.
+- Since dependencies versions in `setup.py` are not pinned, you need to pump the version in order to use a new environment. That environment will then be cached and used by your subsequence commits within the PR, until you pump the version again
+- The new environment created during your PR is cached and will be available to others once the PR is merged.
+- If you are experimenting with new dependencies and want a fresh environment every time, add `[ignore cache]` in your commit message. The CI will create a fresh environment to run your commit and then discard it.
+- If your PR include updated dependencies, the recommended workflow would be:
+  - Doing development as usual.
+  - When you want to run the CI, push a commit with the message containing `[ignore cache]`.
+  - Once the PR is final, pump the version in `__init__.py` and push a final commit not containing `[ignore cache]`.
+
+# Merge PR guideline
+
+- Use squash and merge option
+- 1st line message is the PR title.
+- The text area is the PR description.