Added comments to new workflow definition files.

.github/workflows/mypy_primer_comment.yaml

@@ -1,3 +1,6 @@
+# This workflow runs when the "Run mypy_primer on PR" workflow completes.
+# It downloads the diff from the other workflow instances and creates
+# a summary comment in the PR.
 name: Comment with mypy_primer diff
 
 on:

.github/workflows/mypy_primer_pr.yaml

@@ -1,6 +1,22 @@
+# This workflow runs mypy_primer, a tool that runs pyright on a variety
+# of open-source Python projects that are known to type check with pyright.
+# It builds pyright from the latest PR commit and the merge base of the PR
+# and compares the output of both. It uploads the diffs as an artifact and
+# creates a PR comment with the results (with the help of the
+# mypy_primer_comment action).
+
+# This workflow definition borrows liberally from the mypy repo. The original 
+# workflow was designed to work in a sharded manner where n copies of
+# mypy_primer are started in parallel. Each instance runs 1/n of the projects.
+# For now, we run only one instance because pyright is fast, and the number
+# of projects that use pyright for type checking is small. To change this in
+# the future, change the 'shard_index' matrix to [0, 1, ..., n-1] and set
+# 'num-shards' to n.
+
 name: Run mypy_primer on PR
 
 on:
+  # Run on the creation or update of a PR.
   pull_request:
     paths:
       - 'packages/pyright/**'

.github/workflows/mypy_primer_push.yaml

@@ -1,6 +1,11 @@
+# This workflow runs mypy_primer, a tool that runs pyright on a variety
+# of open-source Python projects that are known to type check with pyright.
+# It builds pyright from the latest commit and the last release tag and
+# compares the output of both. It uploads the diffs as an artifact.
 name: Run mypy_primer on push
 
 on:
+  # Run on all pushes to main.
   push:
     branches:
       - main
@@ -8,6 +13,7 @@ on:
       - 'packages/pyright/**'
       - 'packages/pyright-internal/src/**'
       - 'packages/pyright-internal/typeshed-fallback/**'
+  # Also run manually if requested.
   workflow_dispatch:
 
 concurrency: