Doc updates to install, migration, and after migration sections

[jeremy-moffitt]

Addresses doc feedback from https://github.com/SUSE/suse-migration-services/issues/267 , https://github.com/SUSE/suse-migration-services/issues/266 , and https://github.com/SUSE/suse-migration-services/issues/265

[jeremy-moffitt]

screenshots of the changes, I didn't follow exactly the text in the issues, happy to revisit if the requested approach is preferred

[jeremy-moffitt]

@KeithMnemonic @m0rbo I don't appear to be able to add reviewers, please review when time permits

[jeremy-moffitt]

note that the official docs will have SUSE styling, which is not present in the screenshots here

[jeremy-moffitt]

updated run_migration and kexec sections per feedback

[m0rbo]

The Installation Section 4, option 2 should install both packages: sudo zypper in SLES15-Migration suse-migration-sle15-activation

[jeremy-moffitt]

fixed option2 issue, good catch!

[jeremy-moffitt]

@m0rbo any additional feedback or should we go ahead and merge these changes?

[m0rbo]

@m0rbo any additional feedback or should we go ahead and merge these changes?

LGTM!