lsns: add page

[adrienthebo]

• The page (if new), does not already exist in the repository.
• 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).

Version of the command being documented (if known):

2.37.4

[tldr-bot]

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

pages/linux/lsns.md:
Error: Parse error on line 5:
...es/man8/lsns.8.html>- List all namespa
-----------------------^
Expecting 'END_INFORMATION_LINK_URL', got 'NEWLINE'
pages/linux/lsns.md:3: TLDR003 Descriptions should start with a capital letter
pages/linux/lsns.md:3: TLDR004 Command descriptions should end in a period
pages/linux/lsns.md:4: TLDR003 Descriptions should start with a capital letter
pages/linux/lsns.md:5: TLDR011 Page never contains more than a single empty line

Please fix the error(s) and push again.

[tldr-bot]

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

pages/linux/lsns.md:
Error: Parse error on line 5:
...es/man8/lsns.8.html>- List all namespa
-----------------------^
Expecting 'END_INFORMATION_LINK_URL', got 'NEWLINE'
pages/linux/lsns.md:3: TLDR003 Descriptions should start with a capital letter
pages/linux/lsns.md:3: TLDR004 Command descriptions should end in a period
pages/linux/lsns.md:4: TLDR003 Descriptions should start with a capital letter
pages/linux/lsns.md:5: TLDR011 Page never contains more than a single empty line

Please fix the error(s) and push again.

[tldr-bot]

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

pages/linux/lsns.md:3: TLDR003 Descriptions should start with a capital letter
pages/linux/lsns.md:3: TLDR004 Command descriptions should end in a period
pages/linux/lsns.md:4: TLDR003 Descriptions should start with a capital letter

Please fix the error(s) and push again.

[tldr-bot]

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

pages/linux/lsns.md:3: TLDR004 Command descriptions should end in a period
pages/linux/lsns.md:4: TLDR003 Descriptions should start with a capital letter

Please fix the error(s) and push again.

[mfrw]

A teeny cosmetic suggestion

[mfrw]

LGTM :)