Add comments explaining module lock updates. (#3524)

Co-authored-by: Chandler Carruth <chandlerc@gmail.com>

MODULE.bazel

@@ -2,7 +2,17 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-"""Bazel modules."""
+"""Bazel modules.
+
+If `MODULE.bazel.lock` changes locally, it means the host platform hasn't yet
+been added to the lock file. Running `bazel mod deps` provides a canonical
+update to `MODULE.bazel.lock`; create a PR with those changes in order to
+include the host platform.
+
+Platforms tested with GitHub actions are kept up-to-date. Other platforms may
+fall out of sync on dependency changes, and should be updated with a PR the same
+way a platform is added.
+"""
 
 module(name = "carbon")
 

MODULE.bazel.lock

@@ -1,6 +1,6 @@
 {
   "lockFileVersion": 3,
-  "moduleFileHash": "54dd3881f69c1741aa5508130129b2e828f36e808ee8bdd8324943efc9a5dfe2",
+  "moduleFileHash": "e26dd413860ade9d56f400f7fefc3e9832685fcc4c3b4070479d2e9c5a3cfbd5",
   "flags": {
     "cmdRegistries": [
       "https://bcr.bazel.build/"
@@ -55,7 +55,7 @@
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 48,
+                "line": 58,
                 "column": 13
               }
             },
@@ -81,7 +81,7 @@
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 80,
+                "line": 90,
                 "column": 13
               }
             }
@@ -95,7 +95,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 56,
+            "line": 66,
             "column": 35
           },
           "imports": {
@@ -112,7 +112,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 95,
+            "line": 105,
             "column": 29
           },
           "imports": {
@@ -129,7 +129,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 107,
+            "line": 117,
             "column": 23
           },
           "imports": {
@@ -145,7 +145,7 @@
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 108,
+                "line": 118,
                 "column": 17
               }
             }
@@ -159,7 +159,7 @@
           "usingModule": "<root>",
           "location": {
             "file": "@@//:MODULE.bazel",
-            "line": 114,
+            "line": 124,
             "column": 20
           },
           "imports": {
@@ -177,7 +177,7 @@
               "devDependency": false,
               "location": {
                 "file": "@@//:MODULE.bazel",
-                "line": 115,
+                "line": 125,
                 "column": 10
               }
             }