docs: add public Git error messages

messages/git-error.md

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+# Git: Error
+
+An error occured while syncing models to Prismic from a Git repository.
+
+### How to fix the issue
+
+Syncing the project again by committing to the repository.
+
+If the issue is not resolved, please check the [Prismic Help Center](https://prismic.io/docs/help-center).

messages/git-invalid-slice-machine-config.md

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+# Git: Invalid Slice Machine config
+
+The Git repository's Slice Machine configuration file (`slicemachine.config.json`) was not valid.
+
+Any of the following issues could cause this error:
+
+- Missing required properties, such as `repositoryName` and `adapter`.
+- Invalid values given to configuration properties.
+- Invalid JSON with incorrect syntax
+
+## How to fix the issue
+
+Update the project's Slice Machine configuration file, fixing any syntax errors or incorrect properties.
+
+A basic Slice Machine configuration file looks like this:
+
+```json
+// slicemachine.config.json
+
+{
+  "repositoryName": "example-prismic-repo",
+  "adapter": "@slicemachine/adapter-next",
+  "libraries": ["./src/slices"],
+  "localSliceSimulatorURL": "http://localhost:3000/slice-simulator"
+}
+```

messages/git-unauthorized-github.md

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+# Git: Unauthorized Github access
+
+The GitHub app tried to make a request to GitHub, but failed due to unauthorized access.
+
+This error can occur when your GitHub access token expires. Note that GitHub access tokens are managed for you by installing the Prismic GitHub app and is not something you need to manage manually.
+
+## How to fix the issue
+
+If the error occurs continuously, try the following steps:
+
+1. On GitHub, uninstall the Prismic GitHub app.
+2. In Slice Machine, navigate to the Settings page and re-install the Prismic GitHub app.

messages/git-unauthorized-prismic.md

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+# Git: Unauthorzed Prismic access
+
+The GitHub app tried to make a request to Prismic, but failed due to unauthorized access.
+
+This error can occur when syncing model changes to Prismic from GitHub with an invalid Prismic Write API token.
+
+## How to fix the issue
+
+First, ensure a Prismic Write API token was saved in Slice Machine. You can set, update, and delete a Write API token from Slice Machine's Settings page.
+
+If a token was already saved in Slice Machine, verify that the Prismic Write API token is valid:
+
+1. In the Prismic repository, navigate to the Settings page.
+2. Select **API & Security** in the sidebar and the **Write APIs** tab at the top of the page.
+3. Verify that the Write API token is listed. If necessary, generate a new token and save it in Slice Machine.

messages/git-unsupported-adapter.md

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+# Git: Unsupported adapter
+
+The Slice Machine project uses an adapter that is not supported in the GitHub app.
+
+The following adapters are supported:
+
+- [`@slicemachine/adapter-next`](https://github.com/prismicio/slice-machine/tree/main/packages/adapter-next#readme): Next.js projects
+- [`@slicemachine/adapter-nuxt`](https://github.com/prismicio/slice-machine/tree/main/packages/adapter-nuxt#readme): Nuxt projects
+- [`@slicemachine/adapter-sveltekit`](https://github.com/prismicio/slice-machine/tree/main/packages/adapter-sveltekit#readme): SvelteKit projects
+
+### How to fix the issue
+
+Use a supported adapter.
+
+You can verify which adapter your project uses by checking the `adapter` property in your project's `slicemachine.config.json`.
+
+A basic Slice Machine configuration file looks like this:
+
+```json
+// slicemachine.config.json
+
+{
+  "repositoryName": "example-prismic-repo",
+  "adapter": "@slicemachine/adapter-next",
+  "libraries": ["./src/slices"],
+  "localSliceSimulatorURL": "http://localhost:3000/slice-simulator"
+}
+```
+
+If you would like us to support your adapter, please [open a feature request](https://github.com/prismicio/slice-machine/issues/new/choose).