add /decisions

see https://github.com/joelparkerhenderson/architecture-decision-record

decisions/README.md

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+see [architecture-decision-record](https://github.com/joelparkerhenderson/architecture-decision-record)

decisions/_template.md

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+# Decision record template by Michael Nygard
+
+This is the template in [Documenting architecture decisions - Michael Nygard](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
+You can use [adr-tools](https://github.com/npryce/adr-tools) for managing the ADR files.
+
+In each ADR file, write these sections:
+
+# Title
+
+## Status
+
+What is the status, such as proposed, accepted, rejected, deprecated, superseded, etc.?
+
+## Context
+
+What is the issue that we're seeing that is motivating this decision or change?
+
+## Decision
+
+What is the change that we're proposing and/or doing?
+
+## Consequences
+
+What becomes easier or more difficult to do because of this change?