addpart: add page

[jenesh]

• The page (if new), does not already exist in the repo.
• The page is in the correct platform directory (common/, linux/, etc.)
• The page has 8 or fewer examples.
• The PR title conforms to the recommended templates.
• The page follows the content guidelines.
• The page description includes a link to documentation or a homepage (if applicable).

This PR is in support of #2214.

[CLAassistant]

All committers have signed the CLA.

[tldr-bot]

The build for this PR failed with the following error(s):

pages/linux/addpart.md:3: TLDR004 Command descriptions should end in a period
pages/linux/addpart.md:5: TLDR104 Example descriptions should prefer infinitive tense (e.g. write) over present (e.g. writes) or gerund (e.g. writing)

Please fix the error(s) and push again.

[navarroaxel]

Hi @jenesh, I left some comments.

[navarroaxel]

LGTM

[sbrl]

Thanks, @jenesh!