No environment setup instructions for Met Office users

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

[This documentation page on command line building](https://github.com/MetOffice/lfric_apps/blob/main/documentation/source/developer_guide/local_builds.rst) states "At the Met Office you will need to load the lfric environments before starting the script." but does not currently state what environments these are, or where one might find out. Presumably this means one must run one or more `module load` commands, but it's not clear which. It would be useful to add this information.

### Further details of the issue.

_No response_

Start with documentation/source/developer_guide/local_builds.rst and review the statement about loading LFRic environments at the Met Office. Identify the relevant environment or module-load instructions, then update the page so Met Office users can find and run the required setup commands.

Written by the indexing model from the issue text.