Update the README.md to reflect the '-a' / '--additional-tags' argume…

…nt of 'nf-core download'.

README.md

@@ -437,6 +437,8 @@ Subsequently, the `*.git` folder can be moved to it's final destination and link
 > [!TIP]
 > Also without access to Seqera Platform, pipelines downloaded with the `--platform` flag can be run if the _absolute_ path is specified: `nextflow run -r 2.5 file:/path/to/pipelinedownload.git`. Downloads in this format allow you to include multiple revisions of a pipeline in a single file, but require that the revision (e.g. `-r 2.5`) is always explicitly specified.
 
+Facilities and those who are setting up pipelines for others to use may find the '-a' / '--additional-tag' argument helpful. It must be followed by a string in a "key=value" format and can be provided multiple times. The left-hand side must refer to a valid branch, tag or commit SHA. The right-hand side must comply with the naming conventions for Git tags and may not yet exist in the repository. The '-a' / '--additional-tag' argument allows to customize the downloaded pipeline with additional tags that can be used to select particular revisions in the Seqera Platform interface. For example, an accredited facility may opt to tag particular revisions according to their structured release management process: '-a "3.12.0=testing" -a "3.9.0=validated"' so their staff can easily ensure that the correct version of the pipeline is run in production.
+
 ## Pipeline software licences
 
 Sometimes it's useful to see the software licences of the tools used in a pipeline.