Fix npm install on Ubuntu 24.04

Makefile

@@ -332,7 +332,7 @@ contribs/dist: .build/build-dll.timestamp
 	touch $@
 
 .build/node_modules.timestamp: package.json
-	npm install --omit=optional --legacy-peer-deps
+	NODE_GYP_FORCE_PYTHON=/usr/bin/python npm install --omit=optional --legacy-peer-deps
 	# Installed from peer dependency from ol-layerswitcher and that breaks our types
 	rm -rf ./node_modules/@types/openlayers
 	mkdir -p $(dir $@)

README.md

@@ -32,6 +32,12 @@ GeoMapFish-specific web services. The `gmf` contrib examples are also available
 - [make](https://www.gnu.org/software/make/) – GNU Make.
 - [node](https://www.nodejs.org/) – nodejs JS runtime environment.
 - [npm](https://www.npmjs.com/) – npm package manager.
+- [python](https://www.python.org/) – 3.x installed on the system (be careful with pyenv)
+
+On my Ubuntu 24.04, I had to set the following environment variables to make it work:
+
+- `NODE_GYP_FORCE_PYTHON=/usr/bin/python`
+- `PKG_CONFIG_PATH=/usr/lib/x86_64-linux-gnu/pkgconfig/:/usr/share/pkgconfig/`
 
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