add this recipe for large bulk_inserts to the bulk_insert docs

Migrated issue, originally created by Florian Rüchel (@javex)

I recently had a problem where MySQL would not like to bulk_insert 80k rows at once. Instead I had to feed it 10k chunks. So I split the list into 10k chunks and gave each to alembic.

I don't know if it would make any sense, but I'd suggest adding a parameter chunk_size to bulk_insert. For reference, I did it like this:

    for index, item in enumerate(data):
        if index % 10000 == 0:
            if index != 0:
                op.bulk_insert(table, tmpdata)
            tmpdata = []
        tmpdata.append(item)
if tmpdata:
    op.bulk_insert(GeoIP.__table__, tmpdata)

Let me know what you think of it. I'd be happy to create a patch for it, if you like the idea.

Start with the bulk_insert documentation and the op.bulk_insert example in the issue, then review how the existing Alembic docs organize recipes. Done means documenting the 10,000-row chunking workaround clearly, including the final partial chunk and the MySQL motivation.