Update CONTRIBUTING.md (microsoft#2503)

### Motivation and Context

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Please help reviewers and future users, providing the following
information:
  1. Why is this change required?
  Updating to support questions from community members on plugin hosting
  3. What problem does it solve?
  Provides guidance on SK's repo and plugin
  5. What scenario does it contribute to?
  Plugin and memory plugins created by the community
  7. If it fixes an open issue, please link to the issue here.
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### Description

<!-- Describe your changes, the overall approach, the underlying design.
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### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Devis Lucato <[email protected]>
Co-authored-by: Shawn Callegari <[email protected]>
Co-authored-by: Harleen Thind <[email protected]>

CONTRIBUTING.md

@@ -111,6 +111,32 @@ The scripts below are used to build, test, and lint within the project.
   - Build/Test: `yarn build`
   - Linting (auto-fix): `yarn lint:fix`
 
+### Adding Plugins and Memory Connectors
+
+When considering contributions to plugins and memory connectors for Semantic
+Kernel, please note the following guidelines:
+
+#### Plugins
+
+We appreciate your interest in extending Semantic Kernel's functionality through
+plugins. However, we want to clarify our approach to hosting plugins within our
+GitHub repository. To maintain a clean and manageable codebase, we will not be
+hosting plugins directly in the Semantic Kernel GitHub repository.
+Instead, we encourage contributors to host their plugin code in separate
+repositories under their own GitHub accounts or organization. You can then
+provide a link to your plugin repository in the relevant discussions, issues,
+or documentation within the Semantic Kernel repository. This approach ensures
+that each plugin can be maintained independently and allows for easier tracking
+of updates and issues specific to each plugin.
+
+#### Memory Connectors
+
+For memory connectors, while we won't be directly adding hosting for them within
+the Semantic Kernel repository, we highly recommend building memory connectors
+as separate plugins. Memory connectors play a crucial role in interfacing with
+external memory systems, and treating them as plugins enhances modularity and
+maintainability.
+
 ### PR - CI Process
 
 The continuous integration (CI) system will automatically perform the required