rbash: add page

[zvonimirr]

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

• The page (if new), has been added to the correct platform folder:
  common/ if it's common to all platforms, linux/ if it's Linux-specific, and so on.

• The page has 8 or fewer examples.

• The PR is appropriately titled:
  <command name>: add page for new pages, or <command name>: <description of changes> for pages being edited

• The page follows the contributing guidelines

[tldr-bot]

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

pages/common/rbash.md:3: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:4: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:5: TLDR003 Descriptions should start with a capital letter
pages/common/rbash.md:5: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:6: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:7: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:8: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:9: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:10: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:11: TLDR004 Command descriptions should end in a period
pages/common/rbash.md:28: TLDR008 File should contain no trailing whitespace

Please fix the error(s) and push again.

[agnivade]

We allow only 2 lines for heading. Please update it to have only 2 lines.

[zvonimirr]

Hello, I changed it can you please take a look now?

[agnivade]

Made some changes which clarifies the 2nd line a bit.

[sbrl]

Looks ok to me! Just spotted a teensy grammatical error which I fixed.