libaom: Add README explaining how to create a PR. (#1651)

* libaom: Add README explaining how to create a PR.

This may be a standard process for oss-fuzz and/or github in general,
but it's non-trivial for folks on libaom team, and has been found
to be essential by others in the team.

* Escape angle brackets and capital

projects/libaom/README.md

@@ -0,0 +1,52 @@
+# Submit a Patch to oss-fuzz repo
+
+## One-time Setup
+
+1.  Create github account if needed (with @google.com email address, preferably)
+    and log in.
+1.  To allow “git push” to work, you’ll have to add an SSH key:
+    https://help.github.com/articles/connecting-to-github-with-ssh/
+1.  Go to https://github.com/google/oss-fuzz and click on “Fork”.
+1.  Go to your own fork of the repo, which will be at
+    https://github.com/\<git_username\>/oss-fuzz
+1.  Click on “clone or download” and pick “Clone with SSH” method (I found that
+    easier to use for “git push”). Then copy that URL and run “git clone \<URL\>”
+    in terminal. Now you have a local repo, and **your fork** of the remote repo
+    will be called “**origin**” in your git config.
+1.  Configure a remote repo pointing to the **upstream repo**
+    (https://github.com/google/oss-fuzz) so that it’s called “**upstream**”:
+    *   cd \<local_oss_fuzz_repo_directory\>/oss-fuzz
+    *   git remote add upstream git@github.com:google/oss-fuzz.git
+    *   git remote -v
+
+NOTE: For trivial changes it's possible to edit the files in the web UI on the
+main project and create a commit + pull request from that.
+
+## Workflow for a Pull Request (Patch)
+
+1.  Go to your repo:
+    *   cd \<local_oss_fuzz_repo_directory\>/oss-fuzz
+1.  Create a new branch:
+    *   git checkout master
+    *   git checkout -b new_feature_xyz
+1.  Make your changes and commit them locally with “git commit”
+1.  Push your changes to your fork on github
+    *   git push -u origin HEAD
+    *   (This will create a branch of the same name “new_feature_xyz” on your
+        fork “origin”).
+1.  Open your fork in browser and click on “Compare & pull request” and follow
+    the prompts.
+1.  If changes are requested to the patch:
+    *   make changes to the same local branch
+    *   commit them locally with “git commit” (but DO NOT amend!)
+    *   git push -u origin HEAD
+1.  Once pull request is closed:
+    *   Delete “new_feature_xyz” branch on your fork using the “Delete branch”
+        button on the pull request
+    *   Delete local “new_feature_xyz” branch locally with “git checkout master
+        && git branch -D new_feature_xyz”
+    *   Sync your local repo and your fork with upstream repo:
+        *   git checkout master
+        *   git fetch upstream
+        *   git merge upstream/master
+        *   git push origin master