docs: add spica to adopter organization list (bazel-contrib#2184)

* Add spica to adopter organization list (bazel-contrib#2183)
* docs: update the 'send a PR' link to point to the stable branch

Co-authored-by: Sahin Yort <thesayyn@gmail.com>

README.md

@@ -59,8 +59,9 @@ Organizations:
 - [Webdox](https://www.webdox.cl)
 - [WeMaintain](https://www.wemaintain.com)
 - [LogiOcean](https://www.logiocean.com)
+- [Spica](https://spicaengine.com)
 
-Not on this list? [Send a PR](https://github.com/bazelbuild/rules_nodejs/edit/master/README.md) to add your repo or organization!
+Not on this list? [Send a PR](https://github.com/bazelbuild/rules_nodejs/edit/stable/README.md) to add your repo or organization!
 
 ## User testimonials