Readme: add remarks on CI services free tier vs. "Enterprise" installation

README.md

@@ -57,6 +57,14 @@ levels as the example files.
 
 ## Supported CI Services
 
+The listed properties and instructions for the CI services apply to
+their free tiers for open source projects, hosted in the cloud on
+their infrastructure.
+
+The companies behind these services also offer "enterprise" installations
+on customer infrastructure, which will have different performance
+and limitations.
+
 ### [Travis-CI](https://travis-ci.org/)
  - Five parallel runners on Linux/Windows (one runner on MacOS)
  - Ubuntu 12/14/16/18, MacOS 10.13, Windows Server v1809

appveyor/README.md

@@ -15,6 +15,10 @@
     it to your GitHub account and activate your support module's
     repository. For more details, please see below and refer to the
     [AppVeyor documentation](https://www.appveyor.com/docs/).
+    
+    (This applies when using the free tier offered to open source
+    projects. Things will be different using an "Enterprise"
+    installation on customer hardware.)
 
  2. Add the ci-scripts respository as a Git Submodule
     (see [README](../README.md) one level above).

travis/README.md

@@ -18,6 +18,10 @@
     repository. For more details, please refer to the
     [Travis-CI Tutorial](https://docs.travis-ci.com/user/tutorial/).
     Make sure to use `travis-ci.org` and not their `.com` site.
+    
+    (This applies when using the free tier offered to open source
+    projects. Things will be different using an "Enterprise"
+    installation on customer hardware.)
 
  2. Add the ci-scripts respository as a Git Submodule
     (see [README](../README.md) one level above).