[enh] Add known issues into migration doc

pages/02.administer/15.admin_guide/55.upgrade/15.buster_bullseye/buster_bullseye_migration.fr.md

@@ -89,3 +89,5 @@ yunohost app upgrade --force NOM_APP
 
 ## Soucis (mineurs) connus après la migration
 
+Voir la [page anglaise](https://yunohost.org/en/buster_bullseye_migration#current-known-minor-issues-after-the-migration)
+

pages/02.administer/15.admin_guide/55.upgrade/15.buster_bullseye/buster_bullseye_migration.md

@@ -17,6 +17,8 @@ This page is dedicated to help you migrating an instance from YunoHost 4.4.x (ru
 
 - Please don't rush into thinking that you should need to reinstall your system from scratch thinking it would be "simpler" (sigh). (A common attitude is to be willing to reinstall a server at the slightest complication...) Instead, if you happen to run into issues, we encourage you to try to investigate and understand what's going on and [reach for help on the chat and the forum](/help).
 
+- **You should watch the known issues at the bottom of this page, to be sure your migrations will work properly.**
+
 ## Migration procedure
 
 #### From the webadmin
@@ -88,5 +90,33 @@ If your app is broken and you were already with the last version, you can rerun
 yunohost app upgrade --force APP_NAME
 ```
 
-## Current known (minor) issues after the migration
+## Current known issues after the migration
+
+### Can't run the migration due to `libc6-dev : Breaks: libgcc-8-dev issue`.
+
+You have an app that depends of build-essential package.
+
+See this [solution](https://forum.yunohost.org/t/migration-to-11-wont-start-libc6-dev-breaks-libgcc-8-dev/20617/42) to fix it manually
+
+### DNSmasq is not running anymore
+
+We haven't yet a solution for this issues.
+
+### No ethernet connexion after a reboot after the migration on a rpi 4
+
+! If you have not yet rebooted your server, don't do it we are searching a solution, to avoid the use of a keyboard and screen.
+
+We found this in Rpi documentation
+```
+when the dhcpcd5 package is updated to the latest version (1:8.1.2-1+rpt1 -> 1:8.1.2-1+rpt2), the Raspberry Pi will fail to obtain a DHCP IP address following the next reboot or startup. This problem can be avoided by disabling and re-enabling the "System Options -> Network at Boot" option using the latest raspi-config after the dhcpcd5 package has been updated and prior to the system being shutdown or rebooted
+```
+
+### Restore ynh4 backup onto a fresh ynh11
+
+If you can't restore your app but your system has been restored, you probably should use the regen conf to fix the nginx issues:
+```
+yunohost tools regenconf nginx --force
+```
+
+After what you should be able to restore your apps. Don't forget to force upgrade theme if you have 502 errors.