Create FAQ to address common issues

[jsdw]

There appear to be common themes amoung many of the issues submitted to this repository, including:

• Issues that would be resolved by rebuilding against latest metadata
• Issues that require custom Extra config, (or other customisation)

The error messages that people run into can be confusing, and it's often not imemdiately obvious how to resolve them.

Some of this can (and should where possible) be addressed by code changes, but until then we might be able to reduce the volume of new issues by providing an FAQ which highlights common errors that can occur, and fixes for them.

This should be made as visible as possible when people come to report new issues, so perhaps it could be linked to as part of the default "New Issue" template to nudge users towards it first.

[jsdw]

Eg: #399 (comment) (solution; regenerate metadata)

[jsdw]

Will think about this in #898 and close here