more installation instructions

docs/installation.md

@@ -5,24 +5,33 @@
 ### From F-Droid
 The recommended way of installing is using F-droid. It will automatically manage downloads and keep TT9 up-to-date. The downside is new versions may become available as late as two weeks after the official release.
 
-If you have F-droid, just search for "Traditional T9" and install it. If not, get the official F-droid APK from https://f-droid.org/ and follow the [installation instructions](https://f-droid.org/en/docs/Get_F-Droid/).
+If you don't have F-droid, get the official F-droid APK from https://f-droid.org/ and install it. For more info, refer to the [installation instructions](https://f-droid.org/en/docs/Get_F-Droid/).
+
+After you get F-droid working, just open it, search for "Traditional T9" and install it.
 
 ### From Github
-If you would like to run the latest version as soon as it is released, go to the Github [Releases section](https://github.com/sspanak/tt9/releases). Then either download the APK on your phone, or download it on a computer and transfer it to the phone. After that, just click or tap to install. If custom APK installation is enabled, it will just work. If not, your phone may show a popup, asking you to grant the installation permission, before proceeding.
+If you would like to run the latest version as soon as it is released, go to the GitHub [Releases section](https://github.com/sspanak/tt9/releases). Then either download the APK on your phone or download it on a computer and transfer it to the phone. After that, just click or tap to install. If custom APK installation is enabled, it will just work. If not, your phone may show a popup, asking you to grant the installation permission, before proceeding.
 
-In some cases, installation permissions are disabled by default, but you can usually enable them by going to: Android Settings → Apps → Settings → Security, then enable "Installation from unknown sources".
+In some cases, installation permissions are disabled by default, but you can usually enable them by going to Android Settings → Apps → Settings → Security, then enabling "Installation from unknown sources".
 
 _The setting name or location may be different on different Android versions. Nevertheless, a quick Google search for your phone make and model, should point you in the right direction._
 
 ## Phones which do not allow installing APKs or do not display TT9 after installation
-Some manufacturers prefer to lock their device and disallow installing or enabling (or both) third party keyboards or apps in general. It is likely to reduce the complaints "my phone isn't working", caused by the custom installed apps. The problem has been discussed [here](https://github.com/sspanak/tt9/issues/455) and [here](https://github.com/sspanak/tt9/issues/198).
+Some manufacturers prefer to lock their devices and disallow installing or enabling (or both) third-party keyboards or apps in general. It is likely to reduce the complaints "my phone isn't working", caused by the manually installed apps. The problem has been discussed [here](https://github.com/sspanak/tt9/issues/455) and [here](https://github.com/sspanak/tt9/issues/198).
 
-An examples of such phones are all models by Sonim, especially since the November 2022 update and some Kyocera models, for example: Kyocera DuraXV Extreme+.
+Examples of such phones include some Kyocera models, for example, the DuraXV Extreme+, ZMI Z1, all models by Sonim, and so on. On Sonim XP3800 and XP5800, there is an "Install from Unknown Sources" option, but since the November 2022 update, the phone will still refuse to install APKs unless they have been sent to and approved by Sonim.
 
 ### Prepare Your Computer
-To install TT9 on such locked devices, you will have to connect your phone to a computer and use a program called "adb" (Android Debug Bridge). If you feel confident using the command-line, follow the instructions below.
+To install TT9 on such locked devices, you will have to connect your phone to a computer and use a program called "adb" (Android Debug Bridge). If you feel confident using the command line, follow the instructions below.
+
+First, go through the [adb quick setup](https://www.xda-developers.com/install-adb-windows-macos-linux/). If you need more detailed info, see the [developer documentation](https://developer.android.com/tools/adb).
+
+### Prepare the Phone
+If you have successfully enabled the Developer Mode while setting up ADB, proceed to the next step.
+
+On older phones, the Developer Mode cannot be enabled by clicking the build number. Instead, it is done by dialing a special code which usually looks like this: `*#*#XXXX#*#*`, where XXXX is some number. Find the code for your phone and dial it. Usually, phones from the same company, running the same Android version, share the same code. For example, the code for Sonim XP3800 also works on XP5800.
 
-Go through the [adb quick setup](https://www.xda-developers.com/install-adb-windows-macos-linux/). If you need more detailed info, see the [developer documentation](https://developer.android.com/tools/adb).
+_The procedure on your phone may be entirely different from the methods described above, but Google is your friend. It should be fairly easy to find how to do it unless your phone is completely locked._
 
 ### Install
 If your phone permits installing APKs, skip this step and install normally. Otherwise, install using: