T.: Document ways for resetting passwords just w standard shell utils

docs/reset-password.md

@@ -4,10 +4,11 @@ Resetting a user's invidious password needs you to edit the database.
 
 Firstly, generate a bcrypt-encrypted hash for the new password you want to set for the user.
 
-This can be done with the `bcrypt` python module, though there are other ways of doing the same.
+This can, for example, be done with the `bcrypt` python module or the `mkpasswd` shell utility (the latter should be preinstalled on most systems):
 
 ```
-python3 -c 'import bcrypt; print(bcrypt.hashpw(b"<INSERT PASSWORD HERE>", bcrypt.gensalt(rounds=10)).decode("ascii"))'
+python3 -c 'import bcrypt; print(bcrypt.hashpw(b"<INSERT PASSWORD HERE>", bcrypt.gensalt(rounds=10)).decode("ascii"))' # python
+mkpasswd --method=bcrypt-a -R 10 # mkpasswd
 ```
 
 To do so, first attach to the database:
@@ -23,3 +24,19 @@ UPDATE users SET password = 'HASH' WHERE email = 'USERNAME';
 ```
 
 After that, the password should be reset.
+
+This script bundles all needed commands so you don't have to enter everything manually every time, and also checks that the username exists before writing to the database:
+```sh
+#!/bin/sh
+set -e
+
+printf 'User ID: '
+read -r ID
+if [ "$(su postgres -c "psql invidious -c \"SELECT email FROM users WHERE email = '$ID';\"" | tail -n 2 | head -n 1)" != '(1 row)' ]; then
+    echo 'Error: User ID does not exist'
+    exit 1
+fi
+
+HASH="$(mkpasswd --method=bcrypt-a -R 10)"
+su postgres -c "psql invidious -c \"UPDATE users SET password = '$HASH' WHERE email = '$ID';\""
+```