doc: how to join a wg?

[mcollina]

It is not clear from the docs how to candidate yourself to join a wg: what is the process?

I think we should add a little section after https://github.com/nodejs/node/blob/master/WORKING_GROUPS.md#starting-a-wg, "joining a WG".

Ref: nodejs/readable-stream#185 (comment)

cc @Fishrock123

[Fishrock123]

@mcollina That depends on the WG, sometimes there will be a governance.md file that specifies this stuff. It may be that we should require that even if it just lists like "to join, please make an issue (or PR)".

[mcollina]

I think we should just add a simple sentence in WORKING_GROUPS.md, "to join make an issue".

[Trott]

@mcollina Different working groups can decide on different ways to handle membership, so it would probably have to be something more like, "To find out how to join a working group, consult the GOVERNANCE.md in the working group's repository."