Update build instructions to include a specific version for oapi-codegen (#183)

* Update build instructions to include a specific version for oapi-codegen

Signed-off-by: Kim Tsao <[email protected]>

* Address review comments

Signed-off-by: Kim Tsao <[email protected]>

---------

Signed-off-by: Kim Tsao <[email protected]>

Author: kim-tsao

README.md

@@ -11,6 +11,14 @@ Issue tracking repo: https://github.com/devfile/api with label area/registry
 
 ## Build
 
+### Prerequisite
+
+The current release relies on [oapi-codegen 1.12.4](https://github.com/deepmap/oapi-codegen/tree/v1.12.4) for OpenAPI source generation. See the [Index Server README](index/server/README.md#source-generation) for more information.
+
+To install, run:
+`go install github.com/deepmap/oapi-codegen/cmd/[email protected]`
+
+### Instructions
 If you want to run the build scripts with Podman, set the environment variable
 `export USE_PODMAN=true`