Move germinate out of staging

docs/how-ubuntu-is-made/concepts/germinate.md

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+(germinate)=
+# About Germinate
+
+Germinate is a package available in Debian and Ubuntu which starts with lists of
+packages (called seeds) and grows them into a full list of packages including
+dependencies and (in additional lists) suggests, recommends, and sources for
+each of these lists.
+
+For instructions on using `germinate`, refer to the
+{manpage}`germinate manual page <germinate(1)>`.
+
+
+## Files you need
+
+The minimum set of seeds is:
+
+* `STRUCTURE`
+* `required`
+* `minimal`
+* `standard`
+* `custom`
+* `blocklist`
+* `supported`
+
+It might be possible to exclude some of these (the full set of seeds for Ubuntu
+is much larger), but this set works and at least some of these are hard-coded
+into `germinate`.
+
+Each required seed is a file that must exist. However, placeholders (empty
+files) can be created for any files you don't want to use.
+
+
+## The STRUCTURE file
+
+`STRUCTURE` is special in that it is not actually a list of packages. Rather it
+is the list of seeds and how they depend on each other.
+
+An example `STRUCTURE` is:
+
+```none
+required:
+minimal: required
+standard: required minimal
+custom:
+blocklist:
+supported:
+```
+
+The first thing on each line is the name of a seed followed by a colon. For any
+seed list so defined, a file of the same name must exist in the same directory
+as the `STRUCTURE` file.
+
+After the colon is a space and a space-separated list of seeds the first seed
+on the line depends on. This is used in generating the output such that each
+seed has a corresponding output list of packages which includes the packages
+and depends in the seed itself, plus any packages and dependencies for the
+seeds listed as dependencies for the seed (recursively).
+
+
+## The blocklist file
+
+`blocklist` is also special in that it doesn't define a list of packages to
+include. Instead it lists packages that will never be included in the output
+of `germinate`.
+
+
+## Seed lists
+
+For each seed used, each package is listed on separate lines in wiki bullet
+list format. E.g.
+
+```none
+ * packagename
+```
+
+Items bulleted in this way are assumed to be packages that should be included.
+Anything that is not a bullet list item is ignored by `germinate`, which means
+additional wiki formatting can be used for headers and text.
+