Updated contributing file with DCO (#48)

Update the contributor file to include a DCO, which are going to require
for all incoming contributions to provide indication that the
contributor has the rights to contribute the code.

I also fixed the formatting of contribution HOWTO, since it was getting
mangled.

Signed-off-by: Madelyn Olson <madelyneolson@gmail.com>

CONTRIBUTING.md

@@ -25,6 +25,46 @@ Issues and pull requests for documentation belong on the placeholderkv-doc repo:
 
 If you are reporting a security bug or vulnerability, see SECURITY.md.
 
+## Developer Certificate of Origin
+
+We respect the intellectual property rights of others and we want to make sure all incoming contributions are correctly attributed and licensed. A Developer Certificate of Origin (DCO) is a lightweight mechanism to do that. The DCO is a declaration attached to every commit. In the commit message of the contribution, the developer simply adds a `Signed-off-by` statement and thereby agrees to the DCO, which you can find below or at [DeveloperCertificate.org](http://developercertificate.org/).
+
+```
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the
+    best of my knowledge, is covered under an appropriate open
+    source license and I have the right under that license to
+    submit that work with modifications, whether created in whole
+    or in part by me, under the same open source license (unless
+    I am permitted to submit under a different license), as
+    Indicated in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including
+    all personal information I submit with it, including my
+    sign-off) is maintained indefinitely and may be redistributed
+    consistent with this project or the open source license(s)
+    involved.
+ ```
+
+We require that every contribution to placeholderkv to be signed with a DCO. We require the usage of known identity (such as a real or preferred name). We do not accept anonymous contributors nor those utilizing pseudonyms. A DCO signed commit will contain a line like:
+
+```
+Signed-off-by: Jane Smith <jane.smith@email.com>
+```
+You may type this line on your own when writing your commit messages. However, if your user.name and user.email are set in your git configs, you can use `git commit` with `-s` or `--signoff` to add the `Signed-off-by` line to the end of the commit message. We also require revert commits to include a DCO.
+
 # How to provide a patch for a new feature
 
 1. If it is a major feature or a semantical change, please don't start coding
@@ -34,14 +74,13 @@ and creating an issue at Github with the description of, exactly, what you want
 to accomplish and why. Use cases are important for features to be accepted.
 Here you can see if there is consensus about your idea.
 
-2. If in step 1 you get an acknowledgment from the project leaders, use the
-   following procedure to submit a patch:
-
-    a. Fork placeholderkv on GitHub ( https://docs.github.com/en/github/getting-started-with-github/fork-a-repo )
-    b. Create a topic branch (git checkout -b my_branch)
-    c. Push to your branch (git push origin my_branch)
-    d. Initiate a pull request on GitHub ( https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/creating-a-pull-request )
-    e. Done :)
+2. If in step 1 you get an acknowledgment from the project leaders, use the following procedure to submit a patch:
+    1. Fork placeholderkv on GitHub ( https://docs.github.com/en/github/getting-started-with-github/fork-a-repo )
+    1. Create a topic branch (git checkout -b my_branch)
+    1. Make the needed changes and commit with a DCO. (git commit -s)
+    1. Push to your branch (git push origin my_branch)
+    1. Initiate a pull request on GitHub ( https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/creating-a-pull-request )
+    1. Done :)
 
 3. Keep in mind that we are very overloaded, so issues and PRs sometimes wait
 for a *very* long time. However this is not a lack of interest, as the project