Copy installation instructions to source

Copy installation instructions from the Dangerzone wiki [1] into the
Dangerzone source. This has several benefits:

1. Devs can update installation instructions as part of a PR.
2. Users can see installation instructions for previous releases.

The last point is important, because we can update our instructions in
the main branch, without affecting the instructions a user follows from
the website (currently pointing to the Dangerzone Wiki).

Refs #240

[1]: https://github.com/freedomofpress/dangerzone/wiki/Installing-Dangerzone

INSTALL.md

@@ -0,0 +1,39 @@
+Dangerzone 0.3 is available for:
+
+- Ubuntu 22.04 (jammy)
+- Debian 11 (bullseye)
+- Fedora 36
+- Fedora 35
+
+### Ubuntu, Debian
+
+Add our repository following [these instructions](https://packagecloud.io/firstlookmedia/code/install#manual-deb), or by running this script:
+
+```
+curl -s https://packagecloud.io/install/repositories/firstlookmedia/code/script.deb.sh | sudo bash
+```
+
+Install Dangerzone:
+
+```
+sudo apt update
+sudo apt install -y dangerzone
+```
+
+### Fedora
+
+Add our repository following [these instructions](https://packagecloud.io/firstlookmedia/code/install#manual-rpm), or by running this script:
+
+```
+curl -s https://packagecloud.io/install/repositories/firstlookmedia/code/script.rpm.sh | sudo bash
+```
+
+Install Dangerzone:
+
+```
+sudo dnf install -y dangerzone
+```
+
+## Build from source
+
+If you'd like to build from source, follow the [build instructions](https://github.com/firstlookmedia/dangerzone/blob/master/BUILD.md).

README.md

@@ -13,7 +13,7 @@ _Read more about Dangerzone in the blog post [Dangerzone: Working With Suspiciou
 
 - Download [Dangerzone 0.3.2 for Mac](https://github.com/firstlookmedia/dangerzone/releases/download/v0.3.2/Dangerzone-0.3.2.dmg)
 - Download [Dangerzone 0.3.2 for Windows](https://github.com/firstlookmedia/dangerzone/releases/download/v0.3.2/Dangerzone-0.3.2.msi)
-- See [installing Dangerzone](https://github.com/firstlookmedia/dangerzone/wiki/Installing-Dangerzone) on the wiki for Linux repositories
+- See [installing Dangerzone](INSTALL.md) for Linux repositories
 
 You can also install Dangerzone for Mac using [Homebrew](https://brew.sh/): `brew install --cask dangerzone`
 

RELEASE.md

@@ -85,6 +85,6 @@ Linux binaries are automatically built and deployed to repositories when a new t
 To publish the release:
 
 - Create a new release on GitHub, put the changelog in the description of the release, and upload the macOS and Windows installers
-- Update the [Installing Dangerzone](https://github.com/firstlookmedia/dangerzone/wiki/Installing-Dangerzone) wiki page
+- Update the [Installing Dangerzone](INSTALL.md) page
 - Update the [Dangerzone website](https://github.com/firstlookmedia/dangerzone.rocks) to link to the new installers
 - Update the brew cask release of Dangerzone with a [PR like this one](https://github.com/Homebrew/homebrew-cask/pull/116319)