seems like i removed that target at some point and forgot to update the
readme. As installing go is os specific let's just check for go instead and
let the user handle the installing.
By getting rid of the PHONY install and bundling the go get with its uses we
can prevent unnecessary go gets in `make build` - this speeds up development as
I run `make generate-fixtures` a lot and fetching dependencies takes
comparatively long.
We also add the `-d` flag to go get to get rid of the deprecation warning
```
go get: installing executables with 'go get' in module mode is deprecated.
To adjust and download dependencies of the current module, use 'go get -d'.
To install using requirements of the current module, use 'go install'.
To install ignoring the current module, use 'go install' with a version,
like 'go install example.com/cmd@latest'.
For more information, see https://golang.org/doc/go-get-install-deprecation
or run 'go help get' or 'go help install'.
```
Until now we expected the .org file to print back to itself - we can't do that
when the input is not pretty printed already - with the introduction of blocks
with unindented content that will be the case.
including org files is more complex - e.g. footnotes need to be namespaced to
their source file. org does this by prefixing each included files footnotes
with a number - but even that is not enough as it doesn't guarantee
uniqueness.
As I don't have a usecase for it, I'll avoid the additional complexity for
now.
