Move the info about the package prefix to the packaging section

It's only relevant to developers/packages, so move it out of the
user targeted docs.

web/dev/package-guidelines.md

@@ -30,3 +30,27 @@ To create such .pyc files in a PKGBUILD for packages which don't do it themselve
 MSYS2_ARG_CONV_EXCL="-p" \
   python -m compileall -o 0 -o 1 -q -s"${pkgdir}" -p"/" "${pkgdir}${MINGW_PREFIX}"
 ```
+
+## The package prefix (hack)
+
+When looking at some of our package recipes you might have seen something like:
+
+```bash
+MSYS2_ARG_CONV_EXCL="--prefix=" \
+  meson \
+    --prefix="${MINGW_PREFIX}" \
+    ...
+```
+
+which results in `meson --prefix=/mingw64 ...` being executed.
+
+`/mingw64` in this case is the UNIX prefix where the package will be installed
+to and in addition is a valid Windows path (a drive relative path, so
+`C:\mingw64`), so the native build tools will concatenate it with DESTDIR and
+copy things to the right place.
+
+In the native Windows world this path doesn't make much sense, as `C:\mingw64`
+likely doesn't match where the software lives, but ideally all native Windows
+tools are relocatable and won't use the prefix at runtime anyway. And if they do
+and happen to call Cygwin tools then the prefix resolves to the correct path
+because the Cygwin root path is relocatable.

web/docs/filesystem-paths.md

@@ -121,27 +121,3 @@ you can use `cygpath`:
 $ /usr/bin/python3 -c "import sys, os; print(sys.argv, os.listdir(sys.argv[1]))" "$(cygpath -u C:/)"
 ['-c', '/c/'] ['$Recycle.Bin', '$SysReset', ...]
 ```
-
-## The package prefix (hack)
-
-When looking at some of our package recipes you might have seen something like:
-
-```bash
-MSYS2_ARG_CONV_EXCL="--prefix=" \
-  meson \
-    --prefix="${MINGW_PREFIX}" \
-    ...
-```
-
-which results in `meson --prefix=/mingw64 ...` being executed.
-
-`/mingw64` in this case is the UNIX prefix where the package will be installed
-to and in addition is a valid Windows path (a drive relative path, so
-`C:\mingw64`), so the native build tools will concatenate it with DESTDIR and
-copy things to the right place.
-
-In the native Windows world this path doesn't make much sense, as `C:\mingw64`
-likely doesn't match where the software lives, but ideally all native Windows
-tools are relocatable and won't use the prefix at runtime anyway. And if they do
-and happen to call Cygwin tools then the prefix resolves to the correct path
-because the Cygwin root path is relocatable.