I've already did, download
GooManager, open app, grant it root privilege when asked, open the top right menu and select "Install OpenRecoveryScript".
If it download and flash successfully, TWRP will be installed on your phone, nothing else happens.
Recently Goo.im has been updating their server and the download might not work, but it should be fixed as of version 2.1.3 (right now it still download 2.1.2 to my phone so wait until it's updated to version 2.1.3 in the Google server).
If not, then you have to use fastboot to install it. I don't have much experience with HTC phones and their HBoot, so I can't help you. You can go to this page for the download link and instructions:
[RECOVERY] TWRP touch recovery v2.6.3.4 - xda-developers
Just make sure to use the right version for your HTC One, there are different carriers version and flashing the wrong one might not work, I'm not sure if it matters with the HTC One in term of recovery, but just to be safe.