Add initial info on how to write a component (#88)

README.md

@@ -1,8 +1,55 @@
 # OpenTelemetry Collector Contrib
 This is a repository for OpenTelemetry Collector contributions that are not part of the
-core repository and core distribution of the Collector.
+[core repository](https://github.com/open-telemetry/opentelemetry-collector) and
+core distribution of the Collector. Typically, these contributions are vendor
+specific receivers/exporters and/or components that are either legacy or are only
+useful to relatively small number of users. 
 
 ## Contributing
-
 If you would like to contribute please read [contributing guidelines](https://github.com/open-telemetry/opentelemetry-collector/blob/master/CONTRIBUTING.md)
 before you begin your work.
+
+## Adding New Components
+Before you start please read the [contributing guidelines](https://github.com/open-telemetry/opentelemetry-collector/blob/master/CONTRIBUTING.md).
+
+Any component (receiver, processor, exporter, or extension) needs to implement 
+the interfaces defined on the [core repository](https://github.com/open-telemetry/opentelemetry-collector).
+Familiarize yourself with the interface of the component that you want to write,
+and use existing implementations as reference.
+
+- Create your component under the proper folder and use
+Go standard package naming recommendations.
+- Use a boiler-plate Makefile that just references the one at top level, 
+ie.: `include ../../Makefile.Common` - this allows you to build your component
+with required build configurations for the contrib repo while avoiding building
+the full repo during development.
+- Each component has its own go.mod file. This allows custom builds of the
+collector to take a limited sets of dependencies - so run `go mod` commands as 
+appropriate for your component.
+- Implement the needed interface on your component by importing the appropriate
+component from the core repo.
 Follow the pattern of existing components regarding
+config and factory soruce files and tests.

+- Implement your component as appropriate. Provide end-to-end tests (or mock 
+backend/client as appropriate). Target is to get 80% of code coverage.
+- Add a README.md on the root of your component describing its configuration 
+and usage, likely referencing some of the yaml files used in the component tests.
+We also suggest that the yaml files used in tests have comments for all available
+configuration settings so users can copy and modify them as needed.
+- Add a `replace` directive at the root `go.mod` file so your component is included
+in the build of the contrib executable. 
+
+### General Recommendations
+Below are some recommendations that apply to typical components. These are not rigid
+rules and there are exceptions to them, but, take care considering when you are 
+not following them.
+
+- Avoid introducing asynchronicity on receivers and exporters. Typically, these
+are general cases that can be better handled via processors (that also can be
+reused by other receivers and exporters).
+- When implementing exporters try to leverage the exporter helpers from the core
+repo, see [exporterhelper package](https://github.com/open-telemetry/opentelemetry-collector/tree/master/exporter/exporterhelper)
+on core repo.
+
+### Questions?
+Reach the Collector community on [gitter](https://gitter.im/open-telemetry/opentelemetry-service)
+if you have further questions.