[JOSS REVIEW] Minor edits to the github-based documentation

[friedue]

• extend the commands for the installation

git clone https://github.com/genome/bam-readcount 
cd bam-readcount
mkdir build
cd build
cmake ..
make

• perhaps link to VAtools

[bebatut]

It could also be added that bam-readcount can be installed via conda and then give some instruction

[apldx]

Good suggestion, @friedue, done. @bebatut, also a great idea about conda, but we will need to update our conda recipe for the new version (looks like it's currently at v0.8 in bioconda), so leaving this open for now.

[ccwang002]

Bioconda is now able to build the latest version of bam-readcount (v1.0.1) bioconda/bioconda-recipes#47911