Add some basic documentation for Legalpad

Summary: Ref T3116. Explain a couple of core use cases and contextualize the app a bit.

Test Plan: Read application help screen and user guide.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T3116

Differential Revision: https://secure.phabricator.com/D9777

src/applications/legalpad/application/PhabricatorApplicationLegalpad.php

@@ -36,6 +36,17 @@ final class PhabricatorApplicationLegalpad extends PhabricatorApplication {
     );
   }
 
+  public function getHelpURI() {
+    return PhabricatorEnv::getDoclink('Legalpad User Guide');
+  }
+
+  public function getOverview() {
+    return pht(
+      '**Legalpad** is a simple application for tracking signatures and '.
+      'legal agreements. At the moment, it is primarily intended to help '.
+      'open source projects keep track of Contributor License Agreements.');
+  }
+
   public function getRoutes() {
     return array(
       '/L(?P<id>\d+)' => 'LegalpadDocumentSignController',

src/docs/user/userguide/legalpad.diviner

@@ -0,0 +1,71 @@
+@title Legalpad User Guide
+@group userguide
+
+Using Legalpad to track agreements and signatures on legal documents.
+
+= Overview =
+
+Legalpad is a simple application for tracking signatures on legal agreements.
+You can add legal documents, users can sign them, and you can keep track of who
+has signed what.
+
+Right now, it is primarily useful for open source projects that have a
+Contributor License Agreement or a similar document which needs to be signed
+before changes can be accepted from contributors. In particular, it has
+integrations into Differential which can block changes from being accepted until
+the author has signed the required documents.
+
+NOTE: Legalpad is a basic application, and missing many of the features of more
+general document signing software. It may be useful to help you do things
+beyond track CLAs, but you should evaluate its capabilities carefully.
+
+Requiring a CLA
+===============
+
+Open source projects often require contributors to sign a license agreement
+before their contributions can be accepted to the project. To require a CLA or
+similar document for an open source project:
+
+  - Create a CLA document in Legalpad.
+  - Create a "Global" Herald rule which triggers "Always".
+  - The rule should take the action "Require legal signatures", specifying
+    your CLA document as the required document.
+
+After you've done this, all new reviews created in Differential by authors who
+have not signed the document will trigger a signature requirement. These reviews
+can not be accepted until the document has been signed.
+
+If the author has already signed all of the required documents, Herald will not
+take any actions. This reduces the amount of noise the CLA process generates for
+regular contributors.
+
+You can require more than one document (to require that they all be signed), if
+you have several agreements that contributors must sign.
+
+Alternatively, if you have several different sets of agreements for different
+projects, you can also choose a more narrow Herald condition than "Always" (for
+example, require a signature only if the revision is against certain
+repositories).
+
+Document-Based Policies
+=======================
+
+If you have a document like an NDA, you can write a policy rule which prevents
+users from seeing content until they sign the document:
+
+  - In any policy control ("Visible To", "Editable By"), choose "Custom Policy".
+  - Add a rule like "Allow signers of legalpad documents: X".
+  - Leave the default rule as "Deny all other users".
+  - Save the policy.
+
+Users will now only be able to take the action (for example, view or edit the
+object) if they have signed the specified documents.
+
+Roadmap
+========
+
+You can find discussion about the Legalpad roadmap here:
+
+https://secure.phabricator.com/T5505
+
+If there are features you'd like to see, let us know.