Update the plugins managment. Add the function 'omz-plugin' (inspired from bash-it)

plugins/available/gb/README.md

@@ -0,0 +1,21 @@
+# `gb` plugin
+
+> A project based build tool for the Go programming language.
+
+See https://getgb.io for the full `gb` documentation
+
+* * * *
+
+- Adds completion support for all `gb` commands.
+- Also supports completion for the [`gb-vendor` plugin](https://godoc.org/github.com/constabulary/gb/cmd/gb-vendor).
+
+To use it, add `gb` to your plugins array:
+```sh
+plugins=(... gb)
+```
+
+## Caveats
+
+The `git` plugin defines an alias `gb` that usually conflicts with the `gb` program.
+If you're having trouble with it, remove it by adding `unalias gb` at the end of your
+zshrc file.