Add DEVELOPMENT.md file

DEVELOPMENT.md

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+# Development
+
+## Publishing new package to Hex without pre-built libvips binary changes
+
+* Bump version and push to master branch
+
+* Create new release at: https://github.com/akash-akya/vix/releases.
+  Github Actions and TravisCI creates pre-compiled NIF artifacts and push to the release.
+  Wait for all the release to be available. Ensure artifacts are created for all Beam
+  NIF versions, like `2.16`, `2.17`
+
+* On local machine, remove existing pre-built package cache and checksum file `rm -rf cache/ priv/* checksum.exs`
+
+* Remove existing compiled files `rm -rf _build/*/lib/vix`
+
+* Generate `checksum.exs` by running:
+  `ELIXIR_MAKE_CACHE_DIR="$(pwd)/cache" MIX_ENV=prod mix elixir_make.checksum --all`
+  This downloads all available artifacts and generates `checksum.exs` file based on it.
+  Check checksum file contents
+
+* Run test to ensure pre-built package pass the test `ELIXIR_MAKE_CACHE_DIR="$(pwd)/cache" mix test`
+
+* Publish Hex package. `mix hex.publish`
+
+
+## Updating pre-built libvips to match with upstream
+
+Repo: https://github.com/akash-akya/sharp-libvips/
+
+* Pull latest **stable** upstream changes
+
+* Apply patches from our repo
+
+* Create a matching tag and push. The tag commit must match to avoid issues
+
+* Github Actions creates a new release based on the tag
+
+* Ensure all required aftifacts are created
+
+* Update release_tag in the `precompiler.exs`
+
+* Test by setting `export VIX_COMPILATION_MODE=PRECOMPILED_LIBVIPS`
+
+* Once tested, commit to master and publish new version