[develop]: Add RRFS-SD chapter to SRW App docs

[gspetro-NOAA]

DESCRIPTION OF CHANGES:

Adds documentation for the RRFS-SD features added to PR #1127 .

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

TESTS CONDUCTED:

None required. Documentation builds on RTD (see check below). Ran the workflow on Hera using the instructions in these docs.

DEPENDENCIES:

PR #1127

DOCUMENTATION:

All documentation.

ISSUE:

Issue #1126

CHECKLIST

• My code follows the style guidelines in the Contributor's Guide
• I have performed a self-review of my own code using the Code Reviewer's Guide
• I have commented my code, particularly in hard-to-understand areas N/A
• My changes need updates to the documentation. I have made corresponding changes to the documentation
• My changes do not require updates to the documentation (explain).
• My changes generate no new warnings
• New and existing tests pass with my changes N/A
• Any dependent changes have been merged and published

CONTRIBUTORS (optional):

@chan-hoo