Add calculation-period to reporting elements

We discussed about this change on Green-Software-Foundation#123 .

Add workload-start-time and calculation-period to SCI reporting elements as optional fields.
It helps us to understand the impact of start times and processing times of workloads on SCI.

Software_Carbon_Intensity/Appendix_A_Further_Information_on_Reporting_Requirements.md

@@ -22,6 +22,8 @@ The following list contains the REQUIRED and OPTIONAL data elements to be report
 | Software or Product Version | metadata/entity-version | MUST | Text | |
 | SCI Specification Version | metadata/sci-version | MUST | Numeric | The version of the SCI specification against which this report is being made. |
 | Date of Calculation | metadata/calculation-date | MUST | Date | Following a format described in [RFC3339], [a subset](https://ijmacd.github.io/rfc3339-iso8601/) of ISO 8601 |
+| Start date of the workload | metadata/workload-start-time | MAY | Timestamp | Following a format described in [RFC3339], [a subset](https://ijmacd.github.io/rfc3339-iso8601/) of ISO 8601 |
+| Processing period for calculation | metadata/calculation-period | MAY | Numeric | Time taken in seconds to complete the process defined by `R`.  |
 | Further information on calculation | metadata/calculation-information | MAY | Text | More information on your calculation methodology can be provided as freetext, or as a URL to an external document or software repository. |
 | Further information on report | metadata/report-information-url | MAY | URL | More information on your calculation methodology MAY be provided, and this MUST be a URL to an external document or software repository.  |
 
@@ -66,6 +68,8 @@ metadata:
   entity-version: '0.1'
   sci-version: 1.0
   calculation-date: '2021-10-20'
+  workload-start-time: '2021-10-20T01:23:45Z'
+  calculation-period: 600
   calculation-information: 'https://github.com/Green-Software-Foundation/software_carbon_intensity'
   report-information-url: 'https://github.com/Green-Software-Foundation/software_carbon_intensity'
 
@@ -90,4 +94,4 @@ metadata:
   calculation-date: '2021-10-20'
   calculation-information: 'https://github.com/Green-Software-Foundation/software_carbon_intensity'
 
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