Manpages: Auto-generate many through ArgsParser

This set was hand-curated, guided by the questions:
- Does it have at least three options, i.e. is the help page
  non-trivial?
- Is the program unusual, i.e. does listing it in Help or on
  man.serenityos.org spread awareness?
- Is the program common, but we only implement a subset of 'common'
  flags?

Base/usr/share/man/man8/usermod.md

@@ -0,0 +1,32 @@
+## Name
+
+usermod
+
+## Synopsis
+
+```sh
+$ usermod [--uid uid] [--gid gid] [--lock] [--unlock] [--home new-home] [--move] [--shell path-to-shell] [--gecos general-info] <username>
+```
+
+## Description
+
+Modify a user account
+
+## Options:
+
+* `--help`: Display help message and exit
+* `--version`: Print version
+* `-u uid`, `--uid uid`: The new numerical value of the user's ID
+* `-g gid`, `--gid gid`: The group number of the user's new initial login group
+* `-L`, `--lock`: Lock password
+* `-U`, `--unlock`: Unlock password
+* `-d new-home`, `--home new-home`: The user's new login directory
+* `-m`, `--move`: Move the content of the user's home directory to the new location
+* `-s path-to-shell`, `--shell path-to-shell`: The name of the user's new login shell
+* `-n general-info`, `--gecos general-info`: Change the GECOS field of the user
+
+## Arguments:
+
+* `username`: Username of the account to modify
+
+<!-- Auto-generated through ArgsParser -->