chore(doc): adding docs for backup and restore

[pawanpraka1]

fixes : openebs/velero-plugin#112

Signed-off-by: Pawan [email protected]

What this PR does?:

adding docs for backup and restore

Checklist:

• Fixes #
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

[codecov-commenter]

Codecov Report

Merging #210 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #210   +/-   ##
======================================
  Coverage    9.82%   9.82%           
======================================
  Files          20      20           
  Lines        1171    1171           
======================================
  Hits          115     115           
  Misses       1055    1055           
  Partials        1       1           

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