gnu: awscli, python-botocore: Add comment about compatibility.

* gnu/packages/python-web.scm (awscli): Mention that it must be updated
together with ...
* gnu/packages/python-xyz.scm (python-botocore): ... this package, and add
similar comment about awscli.

gnu/packages/python-web.scm

@@ -2288,6 +2288,7 @@ supports url redirection and retries, and also gzip and deflate decoding.")
 
 (define-public awscli
   (package
+    ;; Note: updating awscli typically requires updating botocore as well.
     (name "awscli")
     (version "1.18.6")
     (source

gnu/packages/python-xyz.scm

@@ -10979,6 +10979,8 @@ manipulation library.")
     (license license:expat)))
 
 (define-public python-botocore
+  ;; Note: When updating botocore, also make sure that boto3 and awscli
+  ;; are compatible.
   (package
     (name "python-botocore")
     (version "1.15.26")