Update CONTRIBUTING.md with instructions on releasing specs

CONTRIBUTING.md

@@ -91,6 +91,21 @@ cabal configure <package-name> --ghc-options="-Wwarn"
 cabal build <package-name>
 ```
 
+## Publishing specifications
+Pdf specs are stored as attachments to [github releases](https://github.com/input-output-hk/cardano-ledger/releases)
+We can create a release that builds and attaches the latest specs, by triggering the [push-docs github action](https://github.com/input-output-hk/cardano-ledger/blob/master/.github/workflows/push-specs.yml).
+This github action can be triggered by pushing a tag of the pattern: `v[0-9]+\.[0-9]+\.[0-9]+-cardano-ledger-specs`,
+for example: v1.0.0-cardano-ledger-specs
+
+For example, if we decide it's time to publish new versions of docs, and the current latest release is `v2.0.0-cardano-ledger-specs`.
+We can do the following to publish the pdfs under release `v2.1.0-cardano-ledger-specs`:
+```
+git tag v2.1.0-cardano-ledger-specs`
+git push origin v2.1.0-cardano-ledger-specs
+```
+
+This will create a new release that will be available as [latest](https://github.com/input-output-hk/cardano-ledger/releases/latest).
+
 ## Testing the Haskell programs
 
 The tests can be run with cabal.