Add description

.github/workflows/diffcalc.yml

@@ -1,4 +1,42 @@
-name: Difficulty Calculation
+# ## Description
+#
+# Uses [diffcalc-sheet-generator](https://github.com/smoogipoo/diffcalc-sheet-generator) to run two builds of osu and generate an SR/PP/Score comparison spreadsheet.
+#
+# Can be dispatched both via GitHub -> Actions workflow, or via '!diffcalc' in an issue/PR comment.
+#
+# ## Requirements
+#
+# Self-hosted runner with installed:
+# - `docker >= 20.10.16`
+# - `docker-compose >= 2.5.1`
+# - `lbzip2`
+# - `jq`
+#
+# ## Usage
+#
+# The workflow can be run in two ways:
+# 1. Via workflow dispatch.
+# 2. By an owner of the repository posting a pull request or issue comment containing `!diffcalc`.  
+# For pull requests, the workflow will assume the pull request as the target to compare against (i.e. the `OSU_B` variable).  
+# Any lines in the comment of the form `KEY=VALUE` are treated as variables for the generator.
+#
+# ## Google Service Account
+#
+# Spreadsheets are uploaded to a Google Service Account, and exposed with read-only permissions to the wider audience.
+#
+# 1. Create a project at https://console.cloud.google.com
+# 2. Enable the `Google Sheets` and `Google Drive` APIs.
+# 3. Create a Service Account
+# 4. Generate a key in the JSON format.
+# 5. Encode the key as base64 and store as an **actions secret** with name **`DIFFCALC_GOOGLE_CREDENTIALS`**
+#
+# ## Environment variables
+#
+# The default environment may be configured via **actions variables**.
+#
+# Refer to [the sample environment](https://github.com/smoogipoo/diffcalc-sheet-generator/blob/master/.env.sample), and prefix each variable with `DIFFCALC_` (e.g. `DIFFCALC_THREADS`, `DIFFCALC_INNODB_BUFFER_SIZE`, etc...).
+
+name: Run difficulty calculation comparison
 
 run-name: "${{ github.event_name == 'workflow_dispatch' && format('Manual run: {0}', inputs.osu-b) || 'Automatic comment trigger' }}"