Add api-client documentation.

docs/docs/tachi-server/infrastructure/api-clients.md

@@ -0,0 +1,15 @@
+# Tachi API Clients
+
+Tachi lets users create API Keys, such that programs can interact with their account on their behalf. These API Keys have permissions and other things. You can read about that [here](../../api/auth.md).
+
+However, it's common for another programmer to want certain permissions for their client. For example, if I was making a score import hook for Tachi, I would need the `score_submit` permission.
+
+We could ask users to manually create an API Key, copy it into a config file, and hope that they get the permissions right, or we could set up a nice flow.
+
+## OAuth2 Flow
+
+Tachi fully supports OAuth2. When you create a Tachi API Client, you can set a `redirectUri`, which is where your OAuth2 flow will go. You can read about it [here](./oauth2.md).
+
+## Client File Flow
+
+Alternatively, if you're just looking for a nice UI for users to create an API Key with the right permissions, check out the [Client File Flow](./file-flow.md).

docs/mkdocs.yml

@@ -81,6 +81,7 @@ nav:
                 - "tachi-server/infrastructure/logging.md"
                 - "tachi-server/infrastructure/branches.md"
                 - "tachi-server/infrastructure/versions.md"
+                - "tachi-server/infrastructure/api-clients.md"
                 - "tachi-server/infrastructure/oauth2.md"
                 - "tachi-server/infrastructure/file-flow.md"