Swap DCO link for one with documentation

developercertificate.org contains zero information about how to implement, making it not a great link for someone just learning about DCO. Change link to repo for GitHub integration which minimizes need for documentation for both maintainer (just enable integration) and contributor (no `Signed-off-by` obtains a link to the DCO).

Author: mlinksva

_articles/legal.md

@@ -108,7 +108,7 @@ Also, by adding "paperwork" that some believe is unnecessary, hard to understand
 
 Some situations where you may want to consider an additional contributor agreement for your project include:
 
-* Your lawyers want all contributors to expressly accept (_sign_, online or offline) contribution terms, perhaps because they feel the open source license itself is not enough (even though it is!). If this is the only concern, a contributor agreement that affirms the project's open source license should be enough. The [jQuery Individual Contributor License Agreement](https://contribute.jquery.org/CLA/) is a good example of a lightweight additional contributor agreement. For some projects, a [Developer Certificate of Origin](http://developercertificate.org/) can be an even simpler alternative.
+* Your lawyers want all contributors to expressly accept (_sign_, online or offline) contribution terms, perhaps because they feel the open source license itself is not enough (even though it is!). If this is the only concern, a contributor agreement that affirms the project's open source license should be enough. The [jQuery Individual Contributor License Agreement](https://contribute.jquery.org/CLA/) is a good example of a lightweight additional contributor agreement. For some projects, a [Developer Certificate of Origin](https://github.com/probot/dco) can be an even simpler alternative.
 * Your project uses an open source license that does not include an express patent grant (such as MIT), and you need a patent grant from all contributors, some of whom may work for companies with large patent portfolios that could be used to target you or the project's other contributors and users. The [Apache Individual Contributor License Agreement](https://www.apache.org/licenses/icla.txt) is a commonly used additional contributor agreement that has a patent grant mirroring the one found in the Apache License 2.0.
 * Your project is under a copyleft license, but you also need to distribute a proprietary version of the project. You'll need every contributor to assign copyright to you or grant you (but not the public) a permissive license. The [MongoDB Contributor Agreement](https://www.mongodb.com/legal/contributor-agreement) is an example this type of agreement.
 * You think your project might need to change licenses over its lifetime and want contributors to agree in advance to such changes.