docs: Add X-Patchwork-* header documentation

Avoids sending people to the code to find out about this stuff. Include
examples using 'git-send-email', which should cover most folks.

Signed-off-by: Stephen Finucane <stephen@that.guru>

1 files changed, 34 insertions, 0 deletions

diff --git a/docs/usage/headers.md b/docs/usage/headers.md
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+# Hint Headers
+
+Patchwork provides a number of special email headers to control how a patch is
+handled when it is received. The examples provided below use `git-send-email`,
+but custom headers can also be set when using tools like `mutt`.
+
+## `X-Patchwork-Ignore`
+
+Valid values: *
+
+When set, the mere presence of this header will ensure the provided email is
+not parsed by Patchwork. For example:
+
+    $ git send-email --add-header="X-Patchwork-Ignore: test" master
+
+## `X-Patchwork-Delegate`
+
+Valid values: An email address associated with a Patchwork user
+
+If set and valid, the user corresponding to the provided email address will be
+assigned as the delegate of any patch parsed. If invalid, it will be ignored.
+For example:
+
+    $ git send-email --add-header="X-Patchwork-Delegate: a@example.com" master
+
+## `X-Patchwork-State`
+
+Valid values: Varies between deployments. This can usually be one of
+"Accepted", "Rejected", "RFC" or "Awaiting Upstream", among others.
+
+If set and valid, the state provided will be assigned as the state of any patch
+parsed. If invalid, it will be ignored. For example:
+
+    $ git send-email --add-header="X-Patchwork-State: RFC" master