Regarding APM_PATH values

[sogaiu]

This PR suggests filling in values for APM_PATH to be full-paths.

At the time of writing, the docs here mention:

export APM_PATH=/ppm/bin/apm

At least on Linux when I tried with the suggested value, the packages tab of the settings-view would not show totals for any of the package sections [1].

Using a full-path did work however.

The PR suggests prepending the existing value with <pulsar-source> like:

export APM_PATH=<pulsar-source>/ppm/bin/apm

<pulsar-source> was chosen as it is used at the end of the same section in an example:

# from the directory where you are running pulsar source code
<pulsar source>/ppm/bin/apm link

---

[1] Error output in the console was like:

installed-packages-panel.js? [sm]:197 Fetching local packages failed. Error: Fetching local packages failed.
    at createProcessError (/home/user/src/pulsar/node_modules/settings-view/lib/package-manager.js:575:17)
    at /home/user/src/pulsar/node_modules/settings-view/lib/package-manager.js:583:19
    at Function.simpleDispatch (/home/user/src/pulsar/node_modules/event-kit/dist/emitter.js:64:14)
    at Emitter.emit (/home/user/src/pulsar/node_modules/event-kit/dist/emitter.js:257:28)
    at BufferedProcess.handleError (/home/user/src/pulsar/src/buffered-process.js:326:18)
    at ChildProcess. (/home/user/src/pulsar/src/buffered-process.js:315:12)
    at ChildProcess.emit (events.js:315:20)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:275:12)
    at onErrorNT (internal/child_process.js:465:16)
    at processTicksAndRejections (internal/process/task_queues.js:80:21)
(anonymous) @ installed-packages-panel.js? [sm]:197

I believe there were other adverse side-effects as an appropriate apm binary was not being called.

[sogaiu]

@savetheclocktower passed on a tip to try not setting APM_PATH at all.

At least when I tested that on my local Linux installation, that did work 👍

I was also informed that there is a newer set of docs, and it looks like that has similar text regarding APM_PATH on this page.

Happy to modify this PR, close it, and/or open a new PR at the repository for the new docs.