Document the minimum required Linux kernel version

[jpsamaroo]

When attaching to a process with ROCgdb, the following warning is emitted: "warning: The version of the kernel driver does not match the version required by the ROCm debugger library". It would be great if the minimum Linux kernel version supported by ROCdbgapi were documented somewhere (possibly even passed along to the warning message!).

[jpsamaroo]

It appears that, at the moment of writing, the mainline 5.8-rc4 kernel would not be suitable for ROCdbgapi, since the KFD ioctl version is 1.1, while ROCdbgapi's minimum version is 1.3. Clearly, it is expected that users will need to use a non-mainline kernel with ROCdbgapi. However, this is not documented in the README, and I think it really should be, otherwise the first thing most new users will be greeted with (after going through all the steps to install ROCdbgapi/ROCgdb) is an error that their kernel isn't up to date.

[ppanchad-amd]

@jpsamaroo Apologies for the lack of response. Internal ticket has been created to fix documentation. Thanks!