added Alpine Linux build instructions

Compilation:-Alpine-Linux.md

@@ -0,0 +1,152 @@
+# Alpine Linux build instructions
+
+This guide will help you install qBittorrent on Alpine Linux using a combination of packages installed using `apk` and dependencies built using `cmake`.
+
+ℹ️ This guide should work in any [Alpine arch](http://dl-cdn.alpinelinux.org/alpine/latest-stable/main) as long as the required [packages dependencies](https://pkgs.alpinelinux.org) are available to install for that arch. This guide was tested on `x86_64`
+
+ℹ️ This guide will install qBittorrent and dependencies using shared libraries. At the point of writing this guide the latest version of Alpine is `3.13`
+
+The majority of these commands are copy and paste but some can be modified. For example, in the libtorrent section there is a choice between libtorrent `v1` or `v2`. Check the notes and commented commands for more information.
+
+## Build dependencies
+
+These are the build dependencies we need to install using `apk`
+
+```ash
+apk add autoconf automake build-base cmake curl git libtool linux-headers perl pkgconf python3 python3-dev re2c tar
+```
+
+## Application dependencies
+
+These are application dependencies we need to install using `apk`
+
+ℹ️ The `iconv` libraries needed for `libtorrent` v1.2 are built into `/usr/lib/libc.so` so we do not need to install `iconv` as a dependency.
+
+```ash
+apk add icu-dev libexecinfo-dev openssl-dev qt5-qtbase-dev qt5-qttools-dev zlib-dev qt5-qtsvg-dev
+```
+
+## cmake helpful info
+
+This is a reference section with some helpful `cmake` tweaks you can apply if you need to debug or change anything during the build process.
+
+💡 To see the configuration options available you can use this command in the cloned git folder.
+
+```
+cmake -LAH .
+```
+
+ℹ️ To see project specific variables we can do this to see results after a specific option
+
+
+```
+cmake -LAH . | awk '/CMAKE_VERBOSE_MAKEFILE/,EOF'
+```
+
+ℹ️ After you have run at least one configure command you can see and edit the project settings using `ccmake` to have an interactive method.
+
+```bash
+ccmake .
+```
+
+💡 To set `cxx` flags you can add this to your `cmake` commands but it's optional.
+
+For example, these options can be set `-w` - no warnings `-s` - strip unneeded symbols
+
+```bash
+-D CMAKE_CXX_FLAGS="-w -s"
+```
+
+💡 Ninja build is quiet by default. To enable verbose build information you have these options
+
+Pass `--verbose` to the build command (recommended)
+
+```bash
+cmake --build build --verbose
+```
+
+Add it as cmake variable at configure time.
+
+```bash
+-D CMAKE_VERBOSE_MAKEFILE=ON
+```
+
+## Ninja build
+
+⚠️ There is no `apk` version for Alpine `3.12` or greater so we need to build it. It won't take long.
+
+```bash
+git clone --shallow-submodules --recurse-submodules https://github.com/ninja-build/ninja.git ~/ninja && cd ~/ninja
+git checkout "$(git tag -l --sort=-v:refname "v*" | head -n 1)"
+cmake -Wno-dev -B build \
+	-D CMAKE_CXX_STANDARD=17 \
+	-D CMAKE_INSTALL_PREFIX="/usr/local"
+cmake --build build
+cmake --install build
+```
+
+## Boost build files
+
+ℹ️  All we need to bootstrap boost is to download and extract the files. There is nothing to build at this step.
+
+Download and extract the boost files.
+
+```bash
+curl -sNLk https://boostorg.jfrog.io/artifactory/main/release/1.76.0/source/boost_1_76_0.tar.gz -o "$HOME/boost_1_76_0.tar.gz"
+tar xf "$HOME/boost_1_76_0.tar.gz" -C "$HOME"
+```
+
+## Libtorrent
+
+Download and build libtorrent by checking out the `RC_1_2` branch. You can also change the `git checkout` command filter `"v1*"` to `"v2*"` to use the latest version of a specific tag
+
+ℹ️ Any tag can be used to checkout the version you want - https://github.com/arvidn/libtorrent/tags
+
+```bash
+git clone --shallow-submodules --recurse-submodules https://github.com/arvidn/libtorrent.git ~/libtorrent && cd ~/libtorrent
+# git checkout "$(git tag -l --sort=-v:refname "v2*" | head -n 1)" # always checkout the latest release of libtorrent v2
+git checkout "$(git tag -l --sort=-v:refname "v1*" | head -n 1)" # always checkout the latest release of libtorrent v1
+cmake -Wno-dev -G Ninja -B build \
+    -D CMAKE_BUILD_TYPE="Release" \
+    -D CMAKE_CXX_STANDARD=17 \
+    -D Boost_INCLUDE_DIR="$HOME/boost_1_76_0/" \
+    -D CMAKE_INSTALL_LIBDIR="lib" \
+    -D CMAKE_INSTALL_PREFIX="/usr/local"
+cmake --build build
+cmake --install build
+```
+
+## qBittorrent
+
+Build and install qBittorrent
+
+⚠️ If you do not want the GUI you can set `-D GUI=OFF` to only build and install `qbittorrent-nox`
+
+ℹ️ Any tag can be used to checkout the version you want - https://github.com/arvidn/libtorrent/tags
+
+```bash
+git clone --shallow-submodules --recurse-submodules https://github.com/qbittorrent/qBittorrent.git ~/qbittorrent && cd ~/qbittorrent
+git checkout "$(git tag -l --sort=-v:refname | head -n 1)" # always checkout the latest release of qbittorrent
+cmake -Wno-dev -G Ninja -B build \
+    -D CMAKE_BUILD_TYPE="release" \
+    -D CMAKE_CXX_STANDARD=17 \
+    -D Boost_INCLUDE_DIR="$HOME/boost_1_76_0/" \
+    -D CMAKE_CXX_STANDARD_LIBRARIES="/usr/lib/libexecinfo.so" \
+    -D CMAKE_INSTALL_PREFIX="/usr/local"
+cmake --build build
+cmake --install build
+```
+
+Tidy up the downloaded build files
+
+```bash
+cd && rm -rf qbittorrent libtorrent ninja boost_1_76_0 boost_1_76_0.tar.gz
+```
+
+## Post build
+
+You can now run `qbittorrent` as it will be in the path.
+
+```bash
+qbittorrent
+```