eselect, eselect-{repository,locale}: add page (#13228)

* eselect: add page

* eselect-repository: add page

* eselect-locale: add page

pages/linux/eselect.md

@@ -0,0 +1,17 @@
+# eselect
+
+> Gentoo's multi-purpose configuration and management tool.
+> It consists of various modules that take care of individual administrative tasks.
+> More information: <https://wiki.gentoo.org/wiki/Eselect>.
+
+- Display a list of installed modules:
+
+`eselect`
+
+- View documentation for a specific module:
+
+`tldr eselect {{module}}`
+
+- Display a help message for a specific module:
+
+`eselect {{module}} help`