[rb] add Readme for adding and releasing CDP versions

Author: titusfortner

rb/lib/selenium/devtools/README.md

@@ -0,0 +1,14 @@
+### Adding support for new Chromium DevTools Protocol to the Ruby bindings
+
+* Add the latest version number to `/rb/BUILD.bazel`
+* Update `/rb/lib/selenium/devtools/version.rb` with the latest version number
+
+### Releasing selenium-devtools gem
+
+```shell
+ bazel build //rb:selenium-devtools
+```
+
+```shell
+gem push bazel-bin/rb/selenium-devtools.gem
+```