diff --git a/.github/workflows/release-builtins.yml b/.github/workflows/release-builtins.yml
index db013a2..6597070 100644
--- a/.github/workflows/release-builtins.yml
+++ b/.github/workflows/release-builtins.yml
@@ -38,7 +38,7 @@ jobs:
     - name: Check necessity of release
       id: check
       env:
-        PYPI: ${{ github.event.inputs.environment }}
+        PYPI: ${{ github.event.inputs.environment || 'pypy' }}
         REF: ${{ inputs.tag || 'HEAD' }}
       run: |
         case $PYPI in
diff --git a/ua-parser-builtins/README.md b/ua-parser-builtins/README.md
index 8a56823..061f1c7 100644
--- a/ua-parser-builtins/README.md
+++ b/ua-parser-builtins/README.md
@@ -1,7 +1,14 @@
-# Precompiled ruleset for [ua-parser](https://pypi.org/project/ua-parser/)
+# Precompiled ruleset for [ua-parser]
 
 This project does not do anything on its own, nor does it have any
-actual API: it contains the dataset of
-[uap-core](https://github.com/ua-parser/uap-core) pre-compiled for use
-by [ua-parser](https://pypi.org/project/ua-parser/) to decrease
+actual API: it contains the dataset of [uap-core] pre-compiled for use
+by [ua-parser] to decrease
 initialisation times.
+
+The precompiled ruleset is released monthly based on whatever
+[uap-core]'s default branch is at that moment. The [uap-core] commit
+used for creating the compiled ruleset is stored in the `REVISION`
+file at the root of the wheel.
+
+[ua-parser]: https://pypi.org/project/ua-parser/
+[uap-core]: https://github.com/ua-parser/uap-core