Added readme.md to explain how to uplift etcd transitive dependencies

Signed-off-by: Mike Cobbett <[email protected]>

galasa-extensions-parent/dev.galasa.cps.etcd/README.md

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+# The cps etcd extension
+
+This extension provides access to an implementation of a CPS store based based on remotely connecting to an etcd server.
+
+
+## How the packaging works
+
+This extension is perhaps slightly strange in that it doesn't every want to go out to maven central, so any dependencies it needs to run
+must be included in the osgi bundle.
+
+The extension therefore needs to get hold of the transitive dependencies and include them in a 'fat jar' bundle.
+
+If you look at the built bundle (in the `galasa-extensions-parent/dev.galasa.cps.etcd/build/libs` folder) and unpack the jar, you will see that it packs up the dependndency jars in the root of the bundle jar.
+
+There are 2 parts to packaging this extension:
+- The `build.gradle` file downloads everything that it needed to compile, but it also downloads all the transitive dependencies
+- The `bnd.bnd` file which controls which jars are included in the 'fat jar'.
+
+The gradle plugin `biz.aQute.bnd.builder` is used to do the packing-up of the dependency jars, based on the content of the `bnd.bnd` file.
+
+## How to upgrade the dependencies
+
+- Remove the dependencies from the `build.gradle` file which are only there to make sure things are downloaded which can be bundled into the fat jar.
+- Upgrade what you need to in the `build.gradle`. For example, bump the value for the `io.etcd:jetcd-core` bundle might be what you are trying to do.
+- Run the `calculate-transitive-dependencies.sh` script (in the root of this module). This script calculates the transitive depdendencies of everything which is in the build.gradle file. That's why we need to clean the `build.gradle` to contain only the minimum to start with.
+- Move the contents of `temp/dependencies_gradle_imports.txt` to the `build.gradle` file.
+- Move the contents of `temp/dependencies_gradle.txt` into the `bnd.bnd` file.
+
+This should result in a long list of jars which are first downloaded, then packaged into the extension bundle jar.