Add PR template (emscripten-forge#4847)

Author: IsabelParedes

.github/pull_request_template.md

@@ -0,0 +1,52 @@
+## Template A: Checklist for **adding** a package
+
+### Pre-submission Checks
+- [ ] Package requires building for `emscripten-wasm32` platform (not a noarch package), in other words, the package requires compilation.
+
+<!-- If you have a noarch package, we suggest submitting your recipe to https://github.com/conda-forge/staged-recipes/ instead. -->
+
+### Recipe Structure
+Added `recipes/recipes_emscripten/[package-name]/recipe.yaml` with proper structure:
+- [ ] `context` section with `version` (and optionally `name`)
+- [ ] `package` section with name and version using Jinja2 templates
+- [ ] `source` section with:
+  - Source URL is valid and points to archive file (`.tar.gz`, `.tar.bz2`, `.tar.xz`, `.tgz`, or `.zip`)
+  - Source URL contains `${{ version }}` template for version updates
+  - SHA256 hash is correct (verified with `curl -sL <url> | sha256sum`)
+  - Patches (if any) are included in `[package-name]/patches/` directory
+- [ ] `build` section with appropriate script/method
+  - Python packages: `${PYTHON} -m pip install . ${PIP_ARGS}`
+  - R packages: `$R CMD INSTALL $R_ARGS .`
+  - C++ packages: Uses `emcmake`/`emmake` or `emconfigure`/`emmake`
+  - Rust packages: Uses `rust-nightly` and `maturin` or appropriate Rust build tool
+  - Build number is 0
+  - If the script is longer than 3 lines, a *build.sh* is included
+- [ ] `requirements` section (build, host, run as needed)
+- [ ] `tests` section
+  - Python packages: `test_import_[package].py` file created and referenced
+  - C++ packages: Test executable or package_contents test
+  - R packages: Package contents test
+- [ ] `about` section with license, homepage, summary
+
+---
+
+## Template B: Checklist for **updating** a package
+
+- [ ] ⚠️ Bump build number if the version remains unchanged
+- [ ] Or reset build number to 0 if updating the package to a newer version
+
+---
+
+## PR Formatting
+- [ ] PR title follows format: `Add [package-name]` or `Update [package-name] to [version]`
+- [ ] PR description includes:
+  - Version being added/updated
+  - Any special build considerations or patches applied
+
+## Package Details
+- **Package Name**: 
+- **Version**: 
+
+## Build Notes
+<!-- Any special build considerations, patches applied, or issues encountered -->
+