add pull-requests command to readme

Signed-off-by: Doug Hellmann <doug@doughellmann.com>

README.md

@@ -67,3 +67,30 @@ The report is formatted as
       <PR comment count>: <PR URL> [<PR author>] "<PR title>"
 ```
 
+## Pull Request Statistics
+
+The `pull-requests` sub-command produces a CSV report with details of
+pull requests that can be imported into other data analysis tools for
+processing.
+
+```console
+$ gh-review-stats pull-requests -o metal3-io -r metal3-docs
+Using config file: /Users/dhellmann/.gh-review-stats.yml
+..............................................................................................................................................................
+ID,Title,State,Author,URL,Created,Closed,Days to Merge
+179,Add andfasano as approver,merged,hardys,https://github.com/metal3-io/metal3-docs/pull/179,2021-04-26,2021-04-26,0
+174,Update inspection API proposal status,merged,fmuyassarov,https://github.com/metal3-io/metal3-docs/pull/174,2021-04-01,2021-04-01,0
+172,add feruzjon muyassarov as approver,merged,dhellmann,https://github.com/metal3-io/metal3-docs/pull/172,2021-03-19,2021-03-19,0
+169,Add update strategy to Metal3DataTemplate,merged,kashifest,https://github.com/metal3-io/metal3-docs/pull/169,2021-03-16,2021-04-01,16
+166,Update disabling automated cleaning proposal,merged,fmuyassarov,https://github.com/metal3-io/metal3-docs/pull/166,2021-03-04,2021-03-17,13
+164,Add explicit reboot mode options,merged,rdoxenham,https://github.com/metal3-io/metal3-docs/pull/164,2021-02-10,2021-02-24,13
+163,Presentations framework proposal with a sample presentation,merged,hroyrh,https://github.com/metal3-io/metal3-docs/pull/163,2021-02-08,2021-04-28,79
+162,✨ Proposal: node reuse,merged,furkatgofurov7,https://github.com/metal3-io/metal3-docs/pull/162,2021-02-04,2021-03-10,34
+161,design: support automatic secure boot,merged,dtantsur,https://github.com/metal3-io/metal3-docs/pull/161,2021-02-02,2021-02-12,10
+155,Add proposal for supporting external introspection,merged,hardys,https://github.com/metal3-io/metal3-docs/pull/155,2021-01-06,2021-03-19,71
+152,Proposal for new parameters: Disk and NIC in HWCC,merged,Ashughorla,https://github.com/metal3-io/metal3-docs/pull/152,2020-12-16,2021-03-09,83
+149,Add design proposal for label sync mechanism between BMHs and K Nodes,merged,Arvinderpal,https://github.com/metal3-io/metal3-docs/pull/149,2020-11-09,2021-02-17,100
+147,Support for new parameters in HWCC.,merged,Ashughorla,https://github.com/metal3-io/metal3-docs/pull/147,2020-10-30,2021-03-09,130
+138,design: add sub-states,merged,dtantsur,https://github.com/metal3-io/metal3-docs/pull/138,2020-09-21,2021-02-10,141
+```
+