Document how to add a list of values to the config file

[stonecharioteer]

Related to #7803
(Splitting into 2 as suggested by @pradyunsg)

It would be helpful to document how to add a "list" of values to a section in the ini file. This helps generalize the problem defined in the aforementioned issue.

This helps readers learn how to add multiple links to find-links as already documented in the user guide, but also to apply this knowledge into other areas.

Perhaps it would fit as a "protip" sort of section for the config. For example:

It is possible to **append** values to a section within an ini file such as the pip.ini file.

.. code:: ini
    
    [install]
    find-links =
        http://mirror1.example.com
        http://mirror2.example.com

This enables users to add additional values in the order of entry.

[uranusjr]

I’ll go ahead and label as awaiting PR :)

[deveshks]

Hi @uranusjr ,

Can I take up this issue and create a PR for the same? I am thinking of adding a subsection right before https://github.com/pypa/pip/blob/master/docs/html/user_guide.rst#environment-variables like below. This can also resolve #7803

It is possible to **append** values to a section within an ini file such as the pip.ini file. 
This is applicable to appending options like --find-links or --trusted-hosts, 
which can be written on multiple lines:

.. code-block:: ini
    
[global]
find-links =
    http://download.example.com

[install]
find-links =
    http://mirror1.example.com
    http://mirror2.example.com

[install]
trusted-host = 
    https://pypi.org
    https://artifactory.mydomain.com

This enables users to add additional values in the order of entry for such command line args

[uranusjr]

@deveshks Go ahead! Your examples look very nice to me 😄

[deveshks]

Thanks @uranusjr . I have created the PR for the same. Please take a look

[xavfernandez]

Closed by #7918