Created Change dependencies version. (markdown)

Change-dependencies-version..md

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+Changing a dependency version need (most of the time) three changes.
+
+## The declared version.
+
+In the `base_deps_versions` dictionary in https://github.com/kiwix/kiwix-build/blob/master/kiwixbuild/versions.py
+
+This version number is used to create the source and build directory.
+
+## The archive to download.
+
+Changing a version number is not enough, you have to change the archive that will be used for the dependency.
+This is specific to each dependency and it is in each specific dependency file (ie, https://github.com/kiwix/kiwix-build/blob/master/kiwixbuild/dependencies/android_sdk.py for the android sdk).
+The archive specification is declared this way :
+
+```python
+class Source(ReleaseDownload):
+        archive = Remotefile('tools_r25.2.3-linux.zip',
+                             '1b35bcb94e9a686dff6460c8bca903aa0281c6696001067f34ec00093145b560',
+                             'https://dl.google.com/android/repository/tools_r25.2.3-linux.zip')
+```
+
+- The first argument is the name of the archive.
+- The second argument is the sha256sum of the archive.
+- The optional third argument is the url of the archive. If this is not specified, it will download the archive from http://download.kiwix.org/dev/ (using the archive name).
+
+
+## Update the `base_deps_meta_version`
+
+Base dependencies are cached. And so they are not rebuild by the CI every time. To invalidate the cache, kiwix-build use the variable `base_deps_meta_version` (in https://github.com/kiwix/kiwix-build/blob/master/kiwixbuild/versions.py) . If you want to rebuild everything with the new version of the dependency (and you want), you also need to update the `base_deps_meta_version`.