Improve documentation (influxdata#9457)

CONTRIBUTING.md

@@ -14,11 +14,11 @@
 1. Open a new [pull request][].
 
 #### Contributing an External Plugin *(new)*
-Input, output, and processor plugins written for internal Telegraf can be run as externally-compiled plugins through the [Execd Input](plugins/inputs/execd), [Execd Output](/plugins/outputs/execd), and [Execd Processor](plugins/processors/execd) Plugins without having to change the plugin code.
 
-Follow the guidelines of how to integrate your plugin with the [Execd Go Shim](/plugins/common/shim) to easily compile it as a separate app and run it with the respective `execd` plugin. 
-Check out our [guidelines](docs/EXTERNAL_PLUGINS.md#external-plugin-guidelines) on how to build and set up your external plugins to run with `execd`.
+Input, output, and processor plugins written for internal Telegraf can be run as externally-compiled plugins through the [Execd Input](/plugins/inputs/execd), [Execd Output](/plugins/outputs/execd), and [Execd Processor](/plugins/processors/execd) Plugins without having to change the plugin code.
 
+Follow the guidelines of how to integrate your plugin with the [Execd Go Shim](/plugins/common/shim) to easily compile it as a separate app and run it with the respective `execd` plugin.
+Check out our [guidelines](/docs/EXTERNAL_PLUGINS.md#external-plugin-guidelines) on how to build and set up your external plugins to run with `execd`.
 
 #### Security Vulnerability Reporting
 InfluxData takes security and our users' trust very seriously. If you believe you have found a security issue in any of our

README.md

@@ -16,6 +16,8 @@ Telegraf is plugin-driven and has the concept of 4 distinct plugin types:
 
 New plugins are designed to be easy to contribute, pull requests are welcomed
 and we work to incorporate as many pull requests as possible.
+If none of the internal plugins fit your needs, you could have a look at the
+[list of external plugins](EXTERNAL_PLUGINS.md).
 
 ## Try in Browser :rocket:
 
@@ -29,7 +31,7 @@ There are many ways to contribute:
 - [Review code and feature proposals](https://github.com/influxdata/telegraf/pulls)
 - Answer questions and discuss here on github and on the [Community Site](https://community.influxdata.com/)
 - [Contribute plugins](CONTRIBUTING.md)
-- [Contribute external plugins](https://github.com/influxdata/telegraf/tree/master/plugins/inputs/execd/shim) *(experimental)*
+- [Contribute external plugins](docs/EXTERNAL_PLUGINS.md)
 
 ## Minimum Requirements
 

config/README.md

@@ -0,0 +1 @@
+../docs/CONFIGURATION.md

docs/developers/README.md

@@ -0,0 +1 @@
+../../CONTRIBUTING.md