README: document frequent questions regarding gpg and pinentry

README.md

@@ -30,6 +30,7 @@ In order to use Browserpass you must also install a [companion native messaging
 -   [Privacy](#privacy)
 -   [Requested permissions](#requested-permissions)
 -   [FAQ](#faq)
+    -   [Error: Unable to fetch and parse login fields](#error-unable-to-fetch-and-parse-login-fields)
     -   [How to use the same username and password pair on multiple domains](#how-to-use-the-same-username-and-password-pair-on-multiple-domains)
     -   [Why Browserpass on Firefox does not work on Mozilla domains?](#why-browserpass-on-firefox-does-not-work-on-mozilla-domains)
     -   [Why is OTP not supported?](#why-is-otp-not-supported)
@@ -296,6 +297,38 @@ Browserpass extension requests the following permissions:
 
 ## FAQ
 
+### Error: Unable to fetch and parse login fields
+
+If you can see passwords, but unable to fill forms or copy credentials, you likely have issues with your `gpg` setup.
+
+First things first, make sure that `gpg` and some GUI `pinentry` are installed.
+
+-   on macOS many people succeeded with `pinentry-mac`
+-   on Linux [users report](https://github.com/browserpass/browserpass-extension/issues/155) that `pinentry-gnome3` does not work well with GNOME 3 and Firefox, use e.g. `pinentry-gtk-2`
+-   on Windows WSL people succeded with [pinentry-wsl-ps1](https://github.com/diablodale/pinentry-wsl-ps1)
+
+`pinentry` is the application that asks you your password to unlock PGP key when you for example use `pass`.
+
+This application **must be** GUI app, not console-based like `pinentry-tty`.
+
+Ensure that `gpg-agent` process is actually running, if not you need to investigate how to enable it.
+
+Finally configure a GUI pinentry program in `~/.gnupg/gpg-agent.conf`:
+
+```
+pinentry-program /full/path/to/pinentry
+```
+
+You will need to restart `gpg-agent` using: `$ gpgconf --kill gpg-agent`
+
+If Browserpass is unable to locate the proper `gpg` binary, try configuring a full path to your `gpg` in the browser extension settings or in `.browserpass.json` file in the root of your password store:
+
+```json
+{
+    "gpgPath": "/full/path/to/gpg"
+}
+```
+
 ### How to use the same username and password pair on multiple domains
 
 There are several ways to tell Browserpass to use the same pair of credentials on multiple domains, for example how to re-use an existing password entry `amazon.com.gpg` on a `https://amazon.co.uk` website without duplicating your credentials in multiple password files.