README.md: Toolchain and OS specific remarks.

README.md

@@ -24,6 +24,20 @@ See online documentation at https://github.com/blacksphere/blackmagic/wiki
 
 Binaries from the latest automated build are at http://builds.blacksphere.co.nz/blackmagic
 
+Toolchain specific remarks
+==========================
+Most firmware building is done with the most recent suite from https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm.
+If you have a toolchain from other sources and find problems, check if it is a failure of your toolchain and if not open an issue or better provide a pull request with a fix.
+
+OS specific remarks for BMP-Hosted
+==================================
+Most hosted building is done on and for Linux. BMP-hosted for windows can also be build with Mingw on Linux.
+On BSD/Macos, using dev/tty.usbmodemXXX should work but unresolved discussions indicate a hanging open() call on the second invocation. If that happens, try with cu.usbmodemXXX.
+
+Reporting problems
+==================
+Before reporting issues, check against the latest git version. If possible, test against another target /and/or debug probe. Consider broken USB cables and connectors. Try to reproduce with bmp-hosted with at least debug bit 1 set (blackmagic -v 1 ...), as debug messages will be dumped to the starting console. When reporting issues, be as specific as possible!
+
 Sample Session
 =============
 ```console