Add note on semantic versioning to README

README.md

@@ -101,6 +101,27 @@ http = Net::HTTP.new(uri.host, uri.port)
 http.set_debug_output($stdout)
 ```
 
+## Versioning
+
+This library aims to adhere to [Semantic Versioning 2.0.0][semver].
+Violations of this scheme should be reported as bugs. Specifically,
+if a minor or patch version is released that breaks backward
+compatibility, a new version should be immediately released that
+restores compatibility. Breaking changes to the public API will
+only be introduced with new major versions.
+
+As a result of this policy, you can (and should) specify a
+dependency on this gem using the [Pessimistic Version Constraint][pvc] with two digits of precision.
+
+For example:
+
+```ruby
+spec.add_dependency 'multipart-post', '~> 2.1'
+```
+
+[semver]: http://semver.org/
+[pvc]: http://guides.rubygems.org/patterns/#pessimistic-version-constraint
+
 ## License
 
 Released under the MIT license.