[style-guide] do! indents

I suggest to remove the line-break after `do!` for multi-line expressions when using 4-space indents.
`do! ` is 4 characters long and fits into the current alignment scheme.

Some sample code using the current style guide:
```fs
do!
writeRelated
httpClient
host

do!
writeRelated
httpClient
host

if someRelatedDataVals.Length > 0 then
do!
writeRelated
httpClient
host
someRelatedDataVals
```

Suggested fix:

```fs
do! writeRelated
httpClient
host

do! writeRelated
httpClient
host

if someRelatedDataVals.Length > 0 then
do! writeRelated
httpClient
host
someRelatedDataVals
```

Single-line expressions should not be affected, as there is no forced line break. I.e. `do! writeRelated httpClient host` is already fine.

I originally filed this under .NET docs: https://github.com/dotnet/docs/issues/39302