pmb.config.required_programs: add tar

Add tar as it is required for 'pmbootstrap ci' to get the source into
the pmbootstrap chroot.

Reviewed-by: Caleb Connolly <kc@postmarketos.org>
Link: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/%3C20221031111614.1377-2-ollieparanoid@postmarketos.org%3E

README.md

@@ -46,6 +46,8 @@ Issues are being tracked
 * Python 3.6+
 * OpenSSL
 * git
+* ps
+* tar
 
 ## Usage Examples
 Please refer to the [postmarketOS wiki](https://wiki.postmarketos.org) for

pmb/config/__init__.py

@@ -51,7 +51,12 @@ ondev_min_version = "0.2.0"
 # Programs that pmbootstrap expects to be available from the host system. Keep
 # in sync with README.md, and try to keep the list as small as possible. The
 # idea is to run almost everything in Alpine chroots.
-required_programs = ["git", "openssl", "ps"]
+required_programs = [
+    "git",
+    "openssl",
+    "ps",
+    "tar",
+]
 sudo = which_sudo()
 
 # Keys saved in the config file (mostly what we ask in 'pmbootstrap init')