docs setup (#61)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/quickstart.md

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+## Installation
+!!! note "Latest Stable Release"
+    ```
+    pip install ultralytics
+    ```
+??? tip "Development and Contributing"
+    ```
+    git clone https://github.com/ultralytics/ultralytics
+    cd ultralytics
+    pip install -e '.[dev]'
+    ```
+    See contributing section to know more about contributing to the project
+
+
+## CLI
+The command line YOLO interface let's you simply train, validate or infer models on various tasks and versions.
+CLI requires no customization or code. You can simply run all tasks from the terminal
+!!! tip
+    === "Syntax"
+        ```bash
+        yolo task=detect    mode=train  model=s.yaml    epochs=1 ...
+                   ...             ...          ...
+                 segment          infer       s-cls.pt
+                 classify         val         s-seg.pt
+        ```
+
+    === "Example"
+        ```bash
+        yolo task=detect mode=val model=s.yaml 
+        ```
+        TODO:  add terminal screen/gif
+[CLI Guide](#){ .md-button .md-button--primary}
+
+## Python API
+Ultralytics YOLO comes with pythonic Model and Trainer interface. 
+!!! tip
+    ```python
+    import ultralytics
+    from ultralytics import YOLO
+    model = YOLO()
+    model.new("s-seg.yaml") # automatically detects task type
+    model.load("s-seg.pt") # load checkpoint
+    model.train(data="coco128-segments", epochs=1, lr0=0.01, ...)
+    ```
+[API Guide](#){ .md-button .md-button--primary}