chore: add matrix sdk receipts adr

docs/adr/0005-matrix-sdk-receipts-not-working-properly.md

@@ -0,0 +1,40 @@
+# 5. Matrix SDK receipts not working properly
+
+Date: 2023-09-07
+
+## Status
+
+- Issue: [#418](https://github.com/linagora/twake-on-matrix/issues/347)
+
+## Context
+
+```
+Event.receipts() doesn't take into account private rooms/direct chats
+```
+
+## Root cause
+
+There are differents maps for `Event.receipts() - event.dart(L323)` : global, mainThread and byThread
+```
+* Reason: 
+1. Global : Receipts for every events, no specific thread
+2. MainThread : Receipt for the "main" thread, which is the global timeline without any thread events
+3. ByThread : Receipts inside threads
+
+
+`Event.receipts()` is using the global map, which is not updated when a new event is received.
+
+I realized that the global map is not updated when a new event is received, so the receipts are not updated.
+Otherwise, the mainThread map is updated with good and latest informations.
+
+```
+
+## Decision
+
+1. Use `MainThread` map to check if it contains the events informations.
+2. If it doesn't we use the `Global` map to get the receipts informations.
+
+## Consequences
+
+1. Since we use the global map only if the mainThread map doesn't contain the receipts informations, there is no side effect and it will work as before.
+2. If the mainThread and global maps don't contain the receipts informations, we will not be able to display the receipts informations.