docs: contribution: Start writing linux contrib

Also create index.rst inside /intro/contribution/.
Add Linux kernel (upstream) contribution guidelines.
This will help newcomers to understand in a much more
friendly and simpler manner about the process of
upstreaming.

Signed-off-by: Dhruva Gole <goledhruva@gmail.com>

intro/contribution/index.rst

@@ -10,3 +10,4 @@ Contribution
 
    /intro/contribution/git-usage
    /intro/contribution/style
+   /intro/contribution/upstream-guidelines
\ No newline at end of file

intro/contribution/upstream-guidelines.rst

+.. _beagleboard-contribute:
+
+Upstream Kernel Contributions
+#########
+
+.. note::
+    For detailed information on Kernel Developmement checkout the official
+    `kernel.org <https://www.kernel.org/doc/html/latest/>`_
+    kernel docs.
+
+For a person or company who wishes to submit a change to the Linux kernel,
+the process can sometimes be daunting if you’re not familiar with “the system.”
+This text is a collection of suggestions which can help you get started and greatly increase the chances
+of your change being accepted.
+
+.. note:: This version is an unofficial draft and is subject to change.
+
+Pre-requisites
+---------------
+
+The following are the skills that are needed before you actually start to contribute to the linux kernel:
+    - git
+    - C-Programming
+    - Cross-arch Development
+    - Basics of embedded buses (I2C, UART, SPI, etc.)
+    - Device Trees
+    - Drivers in Embedded Systems
+
+More Git!
+---------
+
+It is highly recommended that you go through
+`Git Usage <https://docs.beagleboard.io/contribution/git-usage.html>`_ before starting
+to read and follow these guidelines. You will need to have a proper git setup on your
+computer inorder to effectively follow these steps.
+
+Creating your first patch
+*************************
+
+When you first enter the world of Linux Kernel development from a background in
+contributing over gitlab or github, the terminologies slightly change.
+
+Your Pull Requests (PRs) now become Patches or Patch Series. You no longer just
+go to some website and click on a "Create Pull Request" button. Whatever code/changes you
+want to add will have to be sent as patches via emails.
+
+As an example, let's consider a commit to add the git section to these docs.
+I stage these changes first using ``git add -p``.
+
+.. code-block::
+
+    diff --git a/contribution/contribute.rst b/contribution/contribute.rst
+    index def100b..0af08c5 100644
+    --- a/contribution/contribute.rst
+    +++ b/contribution/contribute.rst
+
+Then, commit the above changes.
+
+**Note:** Don't forget to make your commit message descriptive of the feature
+you are adding or the work that you have done in that commit. The commit
+has to be self explanatory in itself. Link any references if you have used
+and paste any logs to prove your code works or if there is a fix.
+
+.. code-block::
+
+    git commit -vs
+
+    [linux-contrib 3bc0821] contribute.rst: Add git section
+     1 file changed, 27 insertions(+), 1 deletion(-)
+
+Now, let's say we want to send this new feature to upstream kernel. You then have to create
+a patch file using the following command:
+
+.. code-block::
+
+    git format-patch -1 HEAD
+
+    0001-contribute.rst-Add-git-section.patch
+
+This will generate one file that is generally referred to as the patch file.
+This is what you will now be sending upstream inorder to get your patch merged.
+But wait, there are a few more things we need to setup for sending a patch via e-mail.
+That is, ofcourse your email!
+
+For configuring your email ID for sending patches refer to this excellent stackoverflow thread,
+`configure git-send-email
+<https://stackoverflow.com/questions/68238912/how-to-configure-and-use-git-send-email-to-work-with-gmail-to-email-patches-to>`_.
+
+Finally, after you have configured you email properly, you can send out a patch using:
+
+.. code-block::
+    git send-email 0001-contribute.rst-Add-git-section.patch
+
+replacing ofcourse the above patchfile name with whatever was your own patch.
+This command will then ask you ``To whom should the emails be sent (if anyone)?``
+Here, you have to write the email address of the list you want to send out the patch to.
+
+``git send-email`` also has command line options like ``--to`` and ``--cc`` that you can also use
+to add more email addresses of whoever you want to keep in CC. Generally it is a good idea to keep yourself
+in CC.
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