Readme for pot backend [ci skip] (#24233)

* Readme for pot backend [ci skip]

* empty commit to kick ci

bin/i18n/README.md

+## i18n info
+
+#### Building the backend pot file
+
+Building the backend pot file can be done from the command line:
+
+```shell
+❯ clojure -M -m i18n.enumerate cli.pot
+Created pot file at  cli.pot
+Found 1393 forms for translations
+Grouped into 1313 distinct pot entries
+```
+
+This is called from `update-translation-template` which builds frontend, backend, and automagic dashboard pot files and then merges them into one artifact with `msgcat`.
+
+##### Developer information
+
+We use a custom script to build up our backend pot (po template) file. Start a repl from this folder and the work is done in the `src/i18n/enumerate.clj` file.
+
+It uses the very helpful library [Grasp](https://github.com/borkdude/grasp) to use a spec and a list of sources to find all uses of `trs`, `tru`, etc. It returns the forms found from the source, along with metadata that includes the filenames and line numbers.
+
+```clojure
+enumerate=> (def single-file (str u/project-root-directory "/src/metabase/util.clj"))
+#'i18n.enumerate/single-file
+enumerate=> (map (juxt meta identity)
+                 (g/grasp single-file ::translate))
+([{:line 81,
+   :column 13,
+   :uri "file:/Users/dan/projects/work/metabase/src/metabase/util.clj"}
+  (trs
+   "Maximum memory available to JVM: {0}"
+   (format-bytes (.maxMemory (Runtime/getRuntime))))]
+ [{:line 313,
+   :column 33,
+   :uri "file:/Users/dan/projects/work/metabase/src/metabase/util.clj"}
+  (tru "Timed out after {0}" (format-milliseconds timeout-ms))]
+ [{:line 504,
+   :column 26,
+   :uri "file:/Users/dan/projects/work/metabase/src/metabase/util.clj"}
+  (tru "Not something with an ID: {0}" (pr-str object-or-id))])
+```
+
+Pot files can only have a single entry for each string, so these are grouped by the message and then we use the [org.fedorahosted.tennera.jgettext](https://github.com/zanata/jgettext) library to emit the pot file.
+
+You can build quick pot files with the helpful function `create-pot-file!`
+
+```clojure
+enumerate=> (create-pot-file! single-file "pot.pot")
+Created pot file at  pot.pot
+{:valid-usages 3, :entry-count 4, :bad-forms ()}
+```
+
+which will output
+
+```
+# Copyright (C) 2022 Metabase <docs@metabase.com>
+# This file is distributed under the same license as the Metabase package
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: 1.0\n"
+"Report-Msgid-Bugs-To: docs@metabase.com\n"
+"POT-Creation-Date: 2022-07-22 14:03-0500\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+
+#: /Users/dan/projects/work/metabase/src/metabase/sync/analyze/fingerprint/fingerprinters.clj
+msgid "Error generating fingerprint for {0}"
+msgstr ""
+
+#: metabase/util.clj:81
+msgid "Maximum memory available to JVM: {0}"
+msgstr ""
+
+#: metabase/util.clj:313
+msgid "Timed out after {0}"
+msgstr ""
+
+#: metabase/util.clj:504
+msgid "Not something with an ID: {0}"
+msgstr ""
+```
+
+###### Overrides
+
+You'll note that we defined a single file `"/src/metabase/util.clj"` but ended up with an entry from `fingerprinters.clj`. This is because that usage of `trs` is inside of a macro which emits a defrecord. The quoting means that the form doesn't actually match our spec since it has more sequence stuff:
+
+```clojure
+user=> '`(trs "foobar")
+(clojure.core/seq (clojure.core/concat (clojure.core/list (quote user/trs)) (clojure.core/list "foobar")))
+```
+
+More information in the [grasp issue](https://github.com/borkdude/grasp/issues/28). A quick workaround is just including this manual override.