Add readme entry about "how to encrypt with a passphrase"

[AnomalRoil]

In case somebody wants to use a passphrase to encrypt their data before using timelock encryption, the easiest way is to rely on age:

cat secretfile.txt | age -p | ./tle -e -D 1m -o doublyencryptedfile.tle

age will then prompt for a passphrase or provide one.

and to decrypt:

cat doublyencryptedfile.tle | ./tle -d | age -d > plaintextfile.txt

Maybe add some examples in the readme and link to age documentation? It also works with PGP or anything else that's supporting STDIN and STDOUT pipes.

[ardan-bkennedy]

@gerep Let's use this example and link to the age documentation in the Readme.

cat tlock.go | age -p | ./tle -D 3s -o bill.tle
cat bill.tle | ./tle -d | age -d -o bill.go

This would allow someone to try it out right away. Maybe we use the tlock.go file for the other examples as well?