Add .envrc. (#8382)

.envrc

@@ -0,0 +1,12 @@
+# This file is just a nicety for developers who use direnv. When you cd under
+# the Certbot repo, Certbot's virtual environment will be automatically
+# activated and then deactivated when you cd elsewhere. Developers have to have
+# direnv set up and run `direnv allow` to allow this file to execute on their
+# system. You can find more information at https://direnv.net/.
+. venv3/bin/activate
+# direnv doesn't support modifying PS1 so we unset it to squelch the error
+# it'll otherwise print about this being done in the activate script. See
+# https://github.com/direnv/direnv/wiki/PS1. If you would like your shell
+# prompt to change like it normally does, see
+# https://github.com/direnv/direnv/wiki/Python#restoring-the-ps1.
+unset PS1