add CI readme

.circleci/circleci-readme.md

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+CI Debug Notes
+================
+To validate some circleci stuff, I was able to run a “build locally” using the steps below.
+The local build runs in a docker container.
+
+  * (Once) Install circleci client (`brew install circleci`)
+
+  * Convert the “real” config.yml into a self contained (non-workspace) config via:
+
+        circleci config process .circleci/config.yml > .circleci/local-config.yml
+
+  * Run a local build with the following command:
+
+        circleci local execute -c .circleci/local-config.yml --job 'build'
+
+    Typically both commands are run together:
+
+        circleci config process .circleci/config.yml > .circleci/local-config.yml && circleci local execute -c .circleci/local-config.yml --job 'build'
+
+    With the above command, operations that cannot occur during a local build will show an error like this:
+
+      ```
+      ... Error: FAILED with error not supported
+      ```
+
+      However, the build will proceed and can complete “successfully”, which allows you to verify scripts in your config, etc.
+
+      If the build does complete successfully, you should see a happy yellow `Success!` message.
+
+Miscellaneous
+-------------
+
+To allow your CI build to push changes back to github (e.g. release tags, etc), you need to create setup
+ a github "Deploy Key" with write access. The command below will create such a key. Use an empty password.
+ See: https://circleci.com/docs/2.0/add-ssh-key/#steps
+
+    ssh-keygen -m PEM -t rsa -b 4096 -C "[email protected]" -f <project-name>_github_rsa.key
+
+Paste the public key into a new "write" enabled GitHub deploy key with Title: CircleCI Write <project name>
+
+Be sure you check the "Allow write access" option.
+
+    cat <project-name>_github_rsa.key.pub | pbcopy
+
+In the CircleCI Web UI, under Permissions -> SSH Permissions -> Add SSH Key, enter "Hostname": github.com
+
+Paste the private key.
+
+    cat <project-name>_github_rsa.key | pbcopy        
+
+As a sanity check, the private key should end with `-----END RSA PRIVATE KEY-----`.
+
+Also update the `ssh-fingerprints:` tag in your config.yml to append the fingerprint of the write key.