add short usage doc

Emyrk · Emyrk · commit f23d4e7636dc · 2024-01-10T14:00:58.000-06:00
diff --git a/cmd/testidp/README.md b/cmd/testidp/README.md
@@ -0,0 +1,15 @@
+# How to use
+
+Start the idp service:
+```bash
+$ go run main.go
+2024-01-10 16:48:01.415 [info]  stdlib: 2024/01/10 10:48:01 IDP Issuer URL http://127.0.0.1:44517
+2024-01-10 16:48:01.415 [info]  stdlib: 2024/01/10 10:48:01 Oauth Flags
+2024-01-10 16:48:01.415 [info]  stdlib: 2024/01/10 10:48:01 --external-auth-providers='[{"type":"fake","client_id":"f2df566b-a1c9-407a-8b75-480db45c6476","client_secret":"55aca4e3-7b94-44b6-9f45-ecb5e81c560d","auth_url":"http://127.0.0.1:44517/oauth2/authorize","token_url":"http://127.0.0.1:44517/oauth2/token","validate_url":"http://127.0.0.1:44517/oauth2/userinfo","scopes":["openid","email","profile"]}]'
+2024-01-10 16:48:01.415 [info]  stdlib: 2024/01/10 10:48:01 Press Ctrl+C to exit
+```
+
+Then use the flag into your coderd instance:
+```bash
+develop.sh -- --external-auth-providers='[{"type":"fake","client_id":"f2df566b-a1c9-407a-8b75-480db45c6476","client_secret":"55aca4e3-7b94-44b6-9f45-ecb5e81c560d","auth_url":"http://127.0.0.1:44517/oauth2/authorize","token_url":"http://127.0.0.1:44517/oauth2/token","validate_url":"http://127.0.0.1:44517/oauth2/userinfo","scopes":["openid","email","profile"]}]'
+```
