Refine README.md to include how to update config

See also the relates issue https://github.com/ddev/ddev-drupal9-solr/issues/15.

Just want to add that I recently upgraded search_api_solr and was prompted to deploy the new config.zip. Two difficuilties I encountered were:

1. I couldn't find the "Download config.zip" button as seen when you deploy a new server. Eventually I resorted to adding a new search server. However... I found it later under the Operations dropdown menu.

2. How to deploy config.zip is confusing and I found the simplest way to do it for a self-hosted Solr server, running on Debian, was to simply stop the solr.service and copy the extracted files into /var/solr/data/{core-name}/conf/ dir, after making a backup.

One problem is that the docs specifically mention the "search-api-solr:upload-configset" Drush command, which doesn't exist.

@DamienMcKenna that command lives in the search_api_solr_admin module. Perhaps it was not enabled?

Perhaps a section can be made in the readme specifically titled "Updating configuration" or "Updating" to let this process stand out more in the docs or the current section "Updating Solr" can be enriched with a text that sumps up all the scenarios when to do update the config (and how to do this)

For example...

Updating configuration
--------------------------------
You need to update your config in the following scenarios:
1. When you update the module to a newer version
2. When you add a language
2. When you a add a custom Solr Field Type 

Perhaps we can also mention how to deal with custom changes in relation to updating and version control?
Let's say I have added some synonyms to synonyms_nl.txt and are saving my custom config in a folder in the repo (e.g. config/solr) to use that later on in the deployment cycle. As far I understand when I run 'drush solr-gsc' I get a fresh copy of synonyms_nl.txt which does not include my custom additions.

You can implement a hook to get your modifications into each newly generated config.
This way, also the warning on the status report page will disappear.

Feel free to propose patches to enhance the Readme.

Hi,

it is also very confusing in the readme:

Starting from Search API Solr module version 4.2.1 you don't need to deal with
configsets manually anymore. Just enable the `search_api_solr_admin` sub-module
which is part of Search API Solr. Now you create or update your "collections" at
any time by clicking the "Upload Configset" button on the Search API server
details page (see installation steps below), or use `drush` to do this with

The admin module is enabled. But there is no button "Upload Configset" on the server page.

button Get Config works.
button Reload Core -> gives access denied
Is there anything required in the file permissions other than a standard solr install?

The admin module is enabled. But there is no button "Upload Configset" on the server page.

Is there anything required in the file permissions other than a standard solr install?

Yes, the Configset API is only available in Solr Cloud. (Read the Solr documentation.)

From number 4 worked for me on Centos7

2. How to deploy config.zip is confusing and I found the simplest way to do it for a self-hosted Solr server, running on Debian, was to simply stop the solr.service and copy the extracted files into /var/solr/data/{core-name}/conf/ dir, after making a backup.

I'd like to add how I do it on a local ubuntu.

make the folders accessiable:
sudo chown -R {your user}:{your user} /var/solr

now copy the extracted config to /var/solr/data/{core-name}/conf

set the permissions back:
sudo chown -R solr:solr /var/solr