Add "Building From Source" section to README

[subins2000]

This will be useful from a packaging perspective. Related #5

Building From Source

govarnam

# Install go. Minimum 1.16
sudo apt install golang
git clone https://github.com/varnamproject/govarnam.git govarnam
cd govarnam
make
sudo make install
make release # See the resultant zip

schemes

# Install git LFS first
git clone https://github.com/varnamproject/schemes.git schemes
cd schemes
sudo apt install ruby-ffi ruby-sqlite3
./build_libvarnam.sh
./build_all_schemes.sh
sudo ./install_all_schemes.sh
./build_all_packs.sh
./build_zips.sh

# Package those individual zips as language support. So like sudo apt install varnam-ml will add Malayalam support (ml.zip)

govarnam-ibus

git clone https://github.com/varnamproject/govarnam-ibus.git govarnam-ibus
cd govarnam-ibus
sudo apt install libgtk-3-dev libcairo2-dev libglib2.0-dev
make ubuntu-18 # Depends on gtk3.21
make release # See the resultant zip

A user would install from the zip via ./install.sh. See how this is done: https://varnamproject.github.io/download/linux/#manual

You can also look at .github CI files to see how builds are done.