Add LGPL license

Author: brandur

README.md

@@ -3,6 +3,6 @@
 A future home for River's Ruby bindings. For now, the [Gem is registered](https://rubygems.org/gems/riverqueue), but nothing else is done.
 
 ``` sh
-$ gem build .
-$ gem push riverqueue-0.0.0.gem
+$ gem build riverqueue.gemspec
+$ gem push riverqueue-0.0.1.gem
 ```

riverqueue.gemspec

@@ -1,11 +1,11 @@
 Gem::Specification.new do |s|
   s.name        = "riverqueue"
-  s.version     = "0.0.0"
+  s.version     = "0.0.1"
   s.summary     = "A fast job queue for Go"
   s.description = "A fast job queue for Go."
   s.authors     = ["Blake Gentry", "Brandur Leach"]
   s.email       = "brandur@brandur.org"
   s.files       = ["lib/riverqueue.rb"]
   s.homepage    = "https://riverqueue.com"
-  s.license     = nil
+  s.license     = "LGPL-3.0-or-later"
 end