Update README - lock version to master instead of v1.0

[kmanning]

• The README goes into detail about why you should always reference a version in your pipelines
• The initial part of the README when setting up the library shows setting the default version to v1.0
• There's no really good reason to set the default version to v1.0. Either update it to the latest, or update it to master.

[kmanning]

From Jantman:

For what it's worth:

I really, really think that pinning to versions in pipelines (and pretty much everywhere else) is the right thing to do. If that isn't done, inevitably someone will need to agonize between not releasing a potentially-very-useful change or breaking customers' pipelines (perhaps in a non-obvious or dangerous way).

On the other hand...

I've left in my wake a giant pile of READMEs (for projects in various languages) that have installation examples showing really old version numbers. So... short of either (1) including a note after the example to check for the latest version number or (2) having the example literally pin to @<Latest Version - See Link Below>, I'm not sure what the clean solution to this is.