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+Fuel@OPNFV submodule fetching and patching
+==========================================
+
+This directory holds submodule fetching/patching scripts, intended for
+working with upstream Fuel components (fuel-library, ... , fuel-ui) in
+developing/applying OPNFV patches (backports, custom fixes etc.).
+
+The scripts should be friendly to the following 2 use-cases:
+  - development work: easily cloning, binding repos to specific commits,
+    remote tracking, patch development etc.;
+  - to provide parent build scripts an easy method of tracking upstream
+    references and applying OPNFV patches on top;
+
+Also, we need to support at least the following modes of operations:
+  - submodule bind - each submodule patches will be based on the commit ID
+    saved in the .gitmodules config file;
+  - remote tracking - each submodule will sync with the upstream remote
+    and patches will be applied on top of <sub_remote>/<sub_branch>/HEAD;
+
+Workflow (development)
+----------------------
+The standard development workflow should look as follows:
+
+1. Decide whether remote tracking should be active or not:
+   NOTE: Setting the following var to any non-empty str enables remote track.
+   NOTE: Leaving unset will enable remote track for anything but stable branch.
+
+   $ export FUEL_TRACK_REMOTES=""
+
+2. All Fuel sub-projects are registered as submodules. To initialize them, call:
+   If remote tracking is active, upstream remote is queried and latest remote
+   branch HEAD is fetched. Otherwise, checkout commit IDs from .gitmodules.
+
+   $ make sub
+
+3. Apply patches from `patches/<sub-project>/*` to respective submodules via:
+
+   $ make patches-import
+
+   This will result in creation of:
+   - a tag called `${FUEL_MAIN_TAG}-opnfv-root` at the same commit as Fuel@OPNFV
+     upstream reference (bound to git submodule OR tracking remote HEAD);
+   - a new branch `opnfv-fuel` which will hold all the OPNFV patches,
+     each patch is applied on this new branch with `git-am`;
+   - a tag called `${FUEL_MAIN_TAG}-opnfv` at `opnfv-fuel/HEAD`;
+
+4. Modify sub-projects for whatever you need.
+   Commit your changes when you want them taken into account in the build.
+
+5. Re-create patches via:
+
+   $ make patches-export
+
+   Each commit on `opnfv-fuel` branch of each subproject will be
+   exported to `patches/subproject/` via `git format-patch`.
+
+   NOTE: Only commit (-f) submodules when you need to bump upstream ref.
+   NOTE: DO NOT commit patched submodules!
+
+6. Clean workbench branches and tags with:
+
+   $ make clean
+
+7. De-initialize submodules and force a clean clone with:
+
+   $ make deepclean
+
+Workflow (ISO build)
+--------------------
+Parent build scripts require this mechanism to do some fingerprinting,
+so here is the intended flow for all artifacts to be generated right:
+
+1. (Optional) Cached submodules might be fetched from build cache.
+
+2. Submodules are updated
+   We also dump each submodule's git info using repo_info.sh, since
+   we want to collect git refs before patching (i.e. upstream refs).
+
+3. Make target `release` is built
+   This will make sure the modules are in a clean state, put them in cache,
+   then apply the patches.
+
+4. fuel-main's `${FUEL_MAIN_TAG}-opnfv-root` tag is used to determine VERSION info
+   It will accommodate both bound tags and remote tracking references.
+
+Sub-project maintenance
+-----------------------
+1. Adding a new submodule
+   If you need to add another subproject, you can do it with `git submodule`.
+   Make sure that you specify branch (with `-b`), short name (with `--name`)
+   and point it to `upstream/*` directory, i.e.:
+
+   $ git submodule -b stable/mitaka add --name fuel-web \
+     https://github.com/openstack/fuel-web.git upstream/fuel-web