Document manual release of select packages to CHaP (#4878)

Everything is in the title: A small PR adding some documentation about
#4411

docs/site/src/contributor/how/release-process.md

@@ -2,3 +2,17 @@
 
  - Create new page on cardano-wallet's [wiki](https://github.com/cardano-foundation/cardano-wallet/wiki/_new) called `Release vYYYY-MM-DD` by copying contents of the previous releas.
  - Follow the `Release checklist`. Update progress or report obstacles on the thread.
+
+## Releasing packages to CHaP
+
+[CHaP](https://github.com/IntersectMBO/cardano-haskell-packages) or the _Cardano Haskell Packages_ repository is useful to publish _Haskell_ packages relevant to the Cardano ecosystem as this allows standard build tools like `Cabal` to work out-of-the-box with only some configuration to point to the repository in addition to https://hackage.haskell.org
+
+To publish packages on CHaP:
+
+1. Clone the repository locally from https://github.com/cardano-foundation/cardano-haskell-packages/
+2. Run script to create relevant commits, for example to release `cardano-coin-selection` package and its (local) dependencies:
+
+   ```
+   $ scripts/add-from-github.sh https://github.com/cardano-foundation/cardano-wallet 9eb5f59c328163ca061a20f47519686b6f118d74 lib/coin-selection lib/primitive lib/test-utils lib/delta-types lib/crypto-primitives lib/launcher lib/numeric lib/text-class
+   ```
+3. Open a Pull Request on upstream repository (ie. https://github.com/IntersectMBO/cardano-haskell-packages/)