Fix code block in README

[ijnek]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution
A clear and concise description of what the contribution is.

• Fixes a codeblock in the README

Testing performed
Steps taken to test the contribution:

1. Build steps '...'
2. Execution steps '...'

Expected behavior changes
A clear and concise description of how this contribution will change behavior and level of impact.

• API Change: xxx (if applicable)
• Behavior Change: xxx (if applicable)
• Or no impact to behavior

System(s) tested on

• Hardware: [e.g. PC, SP0, MCP750]
• OS: [e.g. Ubuntu 18.04, RTEMS 4.11, VxWorks 6.9]
• Versions: [e.g. cFE 6.6, OSAL 4.2, PSP 1.3 for mcp750, any related apps or tools]

Additional context
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Code contributions
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[ijnek]

I'm new here and it's my first time contribution. Please let me know if I didn't follow some guideline correctly.