docs: Add some tips and tricks

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+Kontemplate tips & tricks
+=========================
+
+
+## Update Deployments when ConfigMaps change
+
+Kubernetes does [not currently][] have the ability to perform rolling updates
+of Deployments and other resource types when `ConfigMap` or `Secret` objects
+are updated.
+
+It is possible to make use of annotations and templating functions in
+Kontemplate to force updates to these resources anyways (assuming that the
+`ConfigMap` or `Secret` contains interpolated variables).
+ 
+For example:
+
+```yaml
+# A ConfigMap that contains some data structure in JSON format
+---
+kind: ConfigMap
+metadata:
+  name: app-config
+data:
+  configFile: {{ .appConfig | json }}
+```
+
+Now whenever the `appConfig` variable changes we would like to update the
+`Deployment` making use of it, too. We can do this by adding a hash of the
+configuration to the annotations of the created `Pod` objects:
+
+```yaml
+
+---
+kind: Deployment
+metadata:
+  name: app
+spec:
+  template:
+    metadata:
+      annotations:
+        configHash: {{ .appConfig | json | sha256sum }}
+    spec:
+      containers:
+        - name: app
+          # Some details omitted ... 
+          volumeMounts:
+            - name: config
+              mountPath: /etc/app/
+      volumes:
+        - name: config
+          configMap:
+            name: app-config
+```
+
+Now if the `ConfigMap` object appears first in the resource files, `kubectl`
+will apply the resources sequentially and the updated annotation will cause
+a rolling update of all relevant pods.
+
+## direnv & pass
+
+Users of `pass` may have multiple different password stores on their machines.
+Assuming that `kontemplate` configuration exists somewhere on the filesystem
+per project, it is easy to use [direnv][] to switch to the correct
+`PASSWORD_STORE_DIR` variable when entering the folder.
+
+[not currently]: https://github.com/kubernetes/kubernetes/issues/22368
+[direnv]: https://direnv.net/
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