docs(env-format): create "checkpoint" version of subject

subjects/devops/env-format-checkpoint/README.md

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+## Env-format
+
+### Instructions
+
+Create a script `env-format.sh`, which will print the environment variables that have the following formats:
+
+- Print the `PWD` value.
+- All the environment variables that have a letter `H` in the name, without printing the value of those variables.
+
+```console
+$ printenv
+SHELL=/bin/bash
+QT_ACCESSIBILITY=1
+NVM_RC_VERSION=
+COLORTERM=truecolor
+HOMEBREW_PREFIX=/home/linuxbrew/.linuxbrew
+DESKTOP_SESSION=i3
+...
+PWD=/home/user
+LOGNAME=user
+MANPATH=/home/linuxbrew/.linuxbrew/share/man:
+XDG_SESSION_DESKTOP=i3
+XAUTHORITY=/run/user/1000/gdm/Xauthority
+WINDOWPATH=2
+SHELL=/bin/bash
+SSH_AGENT_PID=2900
+HOME=/home/user
+HOMEBREW_SHELLENV_PREFIX=/home/linuxbrew/.linuxbrew
+USERNAME=user
+$
+```
+
+Expected output:
+
+```console
+$ ./env-format.sh
+/home/user/Documents/public/sh/tests/student
+SHELL
+SSH_AGENT_PID
+HOMEBREW_SHELLENV_PREFIX
+MANPATH
+XAUTHORITY
+WINDOWPATH
+HOME
+$
+```