Added Contribution Guide

Exhaustive Contribution Guide. Removed Trailing Whitespaces.
Updated index.md. Abandoned accidental commits 25474,
25474 and uploading a new patchset. Corrected code renderings.

v2 (jsmoeller): Update contribution subchapters

Bug-AGL: SPEC-3633

Signed-off-by: Shankho Boron Ghosh <shankhoghosh123@gmail.com>
Change-Id: Ia808adc0208052f0591396860ac776e34070d279
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/25473
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit de81a8b07f8139fa0f65dddffc839b4a5e83dad7)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/25393

1 files changed, 121 insertions, 0 deletions

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+---
+title: Adding Documentation
+---
+
+The [documentation gerrit repository](https://gerrit.automotivelinux.org/gerrit/admin/repos/AGL/documentation)
+contains AGL documentation website template and content, rendering is
+visible at
+[https://automotivegradelinux.readthedocs.io/en/latest/](https://automotivegradelinux.readthedocs.io/en/latest/).
+The documentation site is hosted on
+[readthedocs](https://readthedocs.org/projects/automotivegradelinux/) and
+corresponding builds are mentioned
+[here](https://readthedocs.org/projects/automotivegradelinux/builds/).
+
+## Download Repository
+
+
+Clone with commit-msg hook :
+
+```sh
+$ git clone "ssh://<LFID>@gerrit.automotivelinux.org:29418/AGL/documentation" && scp -p -P 29418 <LFID>@gerrit.automotivelinux.org:hooks/commit-msg "documentation/.git/hooks/"
+```
+
+## Building a local site
+
+1. Change into the directory
+
+    ```sh
+    $ cd documentation
+    ```
+
+2. Install MkDocs and rtd-dropdown theme
+
+    ```sh
+    $ sudo pip install -r requirements.txt
+    ```
+
+3. Serve locally (defaultly rendered at [127.0.0.1:8000/](127.0.0.1:8000/)):
+
+    ```sh
+    $ sudo mkdocs serve
+    ```
+
+Process to **add new or edit existing** markdown files to AGL documentation:
+
+## Directory Structure
+
+Find existing or add new markdowns in the following directory structure.
+
+```sh
+documentation
+├── docs
+│   ├── 0_Getting_Started
+│   │   ├── 1_Quickstart
+│   │   └── 2_Building_AGL_Image
+|   ├── .....
+|   |
+|   ├──<Chapter-Number>_<Chapter-Name>
+|   |   ├──<Subchapter-Number>_<Subchapter-Name>
+|   |   |   ├──<Index-Number>_<Markdown-Title>.md
+|   |   |   ├── .....
+```
+
+## Markdown Formatting
+
+  1. Add following at the start of each markdown :
+
+    ```sh
+    ---
+    title: <enter-title>
+    ---
+    ```
+
+  2. Internal Linking :
+
+    ```sh
+    [<enter-title>](../<Chapter-Number>_<Chapter-Name>/<Subchapter-Number>_<Subchapter-Name>/<Index-Number>_<Markdown-Title>.md)
+    ```
+
+## Test Hyperlinks
+
+[LinkChecker](https://wummel.github.io/linkchecker/) is a tool that
+allows to check all the hyperlinks in the site.
+
+For testing hyperlinks as soon as the local site is running, do:
+
+```sh
+$ linkchecker http://localhost:8000
+```
+
+The ```linkchecker``` output will display the broken link and there location
+in the site.
+
+
+## Submitting changes
+
+1. Install Git Review
+
+    ```sh
+    #recent version of git-review  (>=1.28.0 is required)
+    $ sudo pip3 install git-review 
+    ```
+
+2. Write commit message
+
+    ```sh
+    # track all the new changes
+    $ git add .
+
+    # Write the commit message
+    $ git commit --signoff
+    ```
+
+3. Push changes for review to Gerrit
+
+    ```sh
+    # first time only
+    $ git review -s
+
+    # then to push use
+    $ git review
+    ```
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