(feat) First cut at a developer's guide to help onboarding users.

docs/developer-guide.md

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+# Developer's Guide to using Weaver
+
+This is an in-progress guide for how to use Weaver to develop your own Semantic Convention registry or codegen.
+
+TODO - Add more getting started guides.
+
+## JQ - Tips and Tricks
+
+While JQ is extremely powerful, it can be finicky to use.  For example, fighting instances where JQ decides to repate a structure vs. nest a list can take some getting used to.
+
+Using an explorer tool like [DevToolsDaily JQ playground](https://www.devtoolsdaily.com/jq_playground/) can dramatically improve your debugging journey in crafting the `jq` expressions you use in rendering templates.
+
+To do so we recommend following [Creating a JSON output for your registry](#creating-a-json-output-for-your-registry) and then copy-paste your registry JSON as input into the JQ playground.
+
+## Templates - Tips and Tricks
+
+When designing JINJA templates, you can make use the the `debug` function to output the context of the template at any point in time.  Simply add `{{ debug(ctx.some_variable) }}` do your template and you'll get a
+JSON rendered view of whatever is passed into `debug` at that portion of the template.
+
+## Policies - Tips and tricks
+
+The OPA policy language REGO can be complicated to learn at first.  Using an explorer tool like [The Rego Playground](https://play.openpolicyagent.org) can be a dramatic aide in live debugging policy files and 
+understanding the language.  
+
+To debug `before_resolution` policies, simply take the model YAML files and convert them to JSON (online tools work here) and then copy-paste this data into the "input" of the Rego playground.
+
+To debug `after_resolution` policies, simply follow the [Creating a JSON output for your registry](#creating-a-json-output-for-your-registry) directions and then copy your registry's JSON into the "input" of
+the Rego playground.
+
+## Creating a JSON output for your registry
+
+Many times it's useful to have raw JSON output of your registry for debugging or tooling. To generate this
+output, simply do the following:
+
+```bash
+weaver registry resolve -r <registry> -o resolved-registry.json
+```