Update README to include point release instructions (#536)

Also update project structure while I'm here

- [X] Does not require a CHANGELOG entry

---------

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>
Co-authored-by: Bastian Köcher <git@kchr.de>

README.md

@@ -4,7 +4,7 @@ This repository houses the code required to build the runtimes for Polkadot, Kus
 
 ## Structure
 
-Each leaf folder contains one runtime crate:
+Runtimes can be found in the `relay` and `system-parachains` top-level folders, each leaf folder of which contains one runtime crate:
 
 <!-- Run "tree -I 'target' -d -L 3" and then delete some folders from Polkadot and Kusama. -->
 
@@ -21,8 +21,15 @@ Each leaf folder contains one runtime crate:
     │   └── bridge-hub-polkadot
     ├── collectives
     │   └── collectives-polkadot
-    └── gluttons
-        └── glutton-kusama
+    ├── coretime
+    │   ├── coretime-kusama
+    │   └── coretime-polkadot
+    ├── encointer
+    ├── gluttons
+    │   └── glutton-kusama
+    └── people
+        ├── people-kusama
+        └── people-polkadot
 ```
 
 ## Approval rights
@@ -61,6 +68,19 @@ The release process is building all runtimes and then puts them into a release i
 
 The format of [`CHANGELOG.md`](CHANGELOG.md) is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+### Point releases
+
+In order to release a patch or fix outside the normal release process, some additional steps are needed.
+
+To submit a fix to release `x.y.z` and make a point release:
+
+- Make your changes based on x.y.z
+- Create a branch `x.y.b` from the most recent release, where `b = z + 1` (contact a maintainer)
+- Make a PR against the branch `x.y.b`
+- Trigger the release process manually (contact a maintainer)
+- Check for other planned releases which originally targeted the same semver version and post on the issue letting them know that they should bump
+- Once the release is out, amend the GitHub release and delete all unchanged runtime blobs. Highlight if this release only affects some runtimes (contact a maintainer)
+- Backport your changes to the `CHANGELOG.md` to the main branch
 ## Release guidelines
 
 Here is an overview of the recommended steps.