Add README.md for all top level codegen modules (#86)

# Motivation
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# Content
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# Testing
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# Please check the following before marking your PR as ready for review

- [x] I have added tests for my changes
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Author: caroljung-cg

src/codegen/cli/README.md

@@ -0,0 +1,13 @@
+# Codegen CLI
+A codegen module that handles all `codegen` CLI commands.
+
+### Dependencies
+- [codegen.sdk](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/sdk)
+- [codegen.shared](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/shared)
+
+## Best Practices
+
+- Each folder in `cli` should correspond to a command group. The name of the folder should be the name of the command group. Ex: `task` for codegen task commands.
+- The command group folder should have a file called `commands.py` where the CLI group (i.e. function decorated with `@click.group()`) and CLI commands are defined (i.e. functions decorated with ex: `@task.command()`) and if necessary a folder called `utils` (or a single `utils.py`) that holds any additional files with helpers/utilities that are specific to the command group.
+- Store utils specific to a CLI command group within its folder.
+- Store utils that can be shared across command groups in an appropriate file in cli/utils. If none exists, create a new appropriately named one!

src/codegen/git/README.md

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+# Codegen Git
+A codegen module to supports git operations on codebase.
+
+### Dependencies
+- [codegen.sdk](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/sdk)
+- [codegen.shared](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/shared)

src/codegen/gsbuild/README.md

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+# Codegen GS Build
+A codegen module that builds the codegen SDK.

src/codegen/gscli/README.md

@@ -1,6 +1,2 @@
-# Best Practices
-
-- Each folder in `cli` should correspond to a command group. The name of the folder should be the name of the command group. Ex: `task` for codegen task commands.
-- The command group folder should have a file called `commands.py` where the CLI group (i.e. function decorated with `@click.group()`) and CLI commands are defined (i.e. functions decorated with ex: `@task.command()`) and if necessary a folder called `utils` (or a single `utils.py`) that holds any additional files with helpers/utilities that are specific to the command group.
-- Store utils specific to a CLI command group within its folder.
-- Store utils that can be shared across command groups in an appropriate file in cli/utils. If none exists, create a new appropriately named one!
+# Codegen GS CLI
+This module to be moved out into `src/code_generation`

src/codegen/gscli/utils/__init__.py

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+# Codegen Runner
+A codegen module to run codemods against a Codebase graph with a managed lifecycle.
+
+### Dependencies
+- [codegen.sdk](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/sdk)
+- [codegen.git](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/git)
+- [codegen.shared](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/shared)

src/codegen/runner/README.md

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+# Codegen SDK
+A codegen module that contains the core Codebase graph parsing and manipulation logic.
+
+### Dependencies
+- [codegen.git](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/git)
+- [codegen.shared](https://github.com/codegen-sh/codegen-sdk/tree/develop/src/codegen/shared)

src/codegen/sdk/README.md

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+# Codegen Shared
+A codegen module to contain a miscellaneous set of shared utilities.
+
+### Dependencies
+This module should NOT contain any high level dependencies on other codegen modules.
+It should only depend on standard libraries and other shared utilities.