Adding a readme just so this branch is clear

integrations/docker/images/chip-build-zap/README.md

@@ -0,0 +1,14 @@
+# ZAP
+
+- This image builds `zap` which gets copied into `chip-build-vscode`.
+- `build.sh` has been modified with a special condition to populate `chip-build-zap`'s build context with the hashes of the CHIP repo working tree and target `zap` version in `zapinfo`.
+- `zapinfo` gets copied to the images at `/opt/zap/zapinfo` and has the following format:
+```
+CUSTOM YES|NO "project-chip/connectedhomeip" $chip_sha "project-chip/zap" $zap_sha
+```
+- `CUSTOM YES` denotes that the `--zap=COMMIT_HASH` argument was issued to `build.sh`. `zap` will be installed at the provided hash.
+- `CUSTOM NO` denotes the default path. In this case, the hash of `zap` is obtained from the `zap` submodule in the working tree.
+- In either situation, `zap` is cloned into the image at build time (instead of copying from local sources which may have changes).
+  - Problem: The build does not account for local updates to the submodule in the current working tree.
+    - Solution: Also clone CHIP repo at build time and check against current hash from working tree.
+