Doc: jobs option and package build setting

docs/how-to.md

@@ -0,0 +1,21 @@
+# How To
+
+## Run parallel jobs, allocate cpu cores per job and allocate memory per job
+
+The `--jobs` option of fromager allows to set the maximum number of wheel build jobs to run in parallel. Below is an example which uses the `--jobs` option along with the bootstrap command
+
+`fromager --jobs 4 bootstrap torch`
+
+For this example, the maximum number of jobs fromager will run in parallel is 4.
+
+The `cpu_cores_per_job` is a package setting that allows to scale parallel jobs by available CPU cores. The default value is set to 1 which indicates as many parallel jobs as CPU logical cores.
+Example: `cpu_cores_per_job = 2` indicates allocating 2 cores per job
+This setting should always have value greater than or equal to 1
+
+The `memory_per_job_gb` is a package setting that allows to scale parallel jobs by available virtual memory without swap. The default value is set to 1.0 which indicates that each parallel job requires 1 GB virtual memory
+Example: `memory_per_job_gb = 0.5` indicates that each parallel job requires 512 MB virtual memory
+This setting should always have value greater than or equal to 0.1
+
+The above mentioned options are related to build systems and can be used as a per package setting when multiple cores and significant amount of memory is available on a build system.
+On the other hand, the `--jobs` overrides the default calculations based on the other settings. For example, when someone passes `--jobs 4` then at most 4 processes will run in parallel when building a given wheel, but if they don't use this option, fromager computes a number of jobs and that value can be influenced based on the per-package settings.
+Note that the jobs are all within the context of building a single wheel.

docs/index.rst

@@ -29,6 +29,7 @@ those special cases directly into fromager.
    using.md
    getting-started.rst
    customization.md
+   how-to.md
    hooks.rst
    files.md
    config-reference.rst