Update api.md

Added changes from ipfs-inactive/docs#368

docs/reference/http/api.md

@@ -7,7 +7,7 @@ title: HTTP API
 <!-- TODO: Describe how to change ports and configure the API server -->
 <!-- TODO: Structure this around command groups (dag, object, files, etc.) -->
 
-_Generated on 2019-06-22, from go-ipfs v0.4.21._
+_Generated on 2019-11-05, from go-ipfs v0.4.22._
 
 When an IPFS node is running as a daemon, it exposes an HTTP API that allows
 you to control the node and run the same commands you can from the command
@@ -17,17 +17,19 @@ In many cases, using this API this is preferable to embedding IPFS directly in
 your program — it allows you to maintain peer connections that are longer
 lived than your app and you can keep a single IPFS node running instead of
 several if your app can be launched multiple times. In fact, the `ipfs`
-CLI commands use this API when operating in [online mode](usage.md#going-online).
+CLI commands use this API when operating in online mode.
 
-This document is autogenerated from go-ipfs. For issues and support, check out
-the [ipfs-http-api-docs](https://github.com/ipfs/ipfs-http-api-docs)
-repository on GitHub.
+::: tip
+This document was autogenerated from go-ipfs. For issues and support, check out the [a href="https://github.com/ipfs/ipfs-http-api-docs](ipfs-http-api-docs) repository on GitHub.
+:::
 
 ## Getting started
 
 ### Alignment with CLI commands
 
-[Every command](../commands/) usable from the CLI is also available through
+The HTTP API under `/api/v0/` is an RPC-style API over HTTP, not a REST API.
+
+[Every command](/reference/cli/) usable from the CLI is also available through
 the HTTP API. For example:
 
 ```sh
@@ -85,6 +87,16 @@ flag is the `&encoding=json` query parameter below:
 }
 ```
 
+## HTTP Status Codes
+Status codes used at the RPC layer are simple:
+* `500` - RPC endpoint returned an error
+* `404` - RPC endpoint doesn't exist
+* `400` - Malformed RPC, argument type error, etc
+* `403` - RPC call forbidden
+In other words, `500` means that the function _does_ exist, it just failed internally for some reason. To know that reason, you have to look at the "application layer" error (commands lib error).
+
+## HTTP Commands
+
 ## /api/v0/add
 
 Add a file or directory to ipfs.