build diagram - external libs do not need our own perl

[shawnlaffan]

The diagram of the build can be updated for the docker process.

While some of the external libs need perl to build, this is currently part of the docker container. If someone is building outside docker then they can use a pre-existing perl, for example a previous Strawberry distribution. I don't think any of the libs require the perl they were built with when they are later used.

This will linearise the whole diagram.

I'll work up a PR when I get a chance.

[genio]

The libraries for Postgresql require Perl to be built. I'm not sure there are any others.

[shawnlaffan]

I'm looking at the Postgres builds, see StrawberryPerl/build-extlibs#36