Signed-off-by: Nemmanuel-ferdman <35470921+emmanuel-ferdman@users.noreply.github.com>

I had to dig into #2410 to learn about the `PROFILE=/dev/null` technique to install without appending to my shell config. Figured this note would be good to add in the main installation docs.
Also added a note on how to do this as a one-liner which was not obvious for me.

Fixes #3104

Fixes #3035

the `nvm.sh` file assigns and exports an `NVM_CD_FLAGS` variable if it
was sourced from a zsh shell. the fact that it's exported means that
it'll be assigned in all child processes, including the `nvm-exec`
script, which uses bash as the interpreter.

Bash's `cd` command doesn't have a `-q` flag, so if the `NVM_CD_FLAGS`
is assigned `-q`, the script will error out and incorrectly claim that
the node version isn't installed.

this also manifests itself in the `nvm exec` command.

Example:

```console
$ nvm exec 16.14.0 npm --version
Running node v16.14.0 (npm v8.3.1)
/Users/<ME>/.nvm/nvm.sh: line 28: cd: -q: invalid option
cd: usage: cd [-L|[-P [-e]] [-@]] [dir]
both the tree and the node path are required
N/A: version "v16.14.0 -> N/A" is not yet installed.

You need to run "nvm install v16.14.0" to install it before using it.
```

To address this, we unset the `NVM_CD_FLAGS` at the start of the
`nvm-exec` script, before loading `nvm.sh`.

Resolves #3081

travis-ci.org is deprecated and replaced by app.travis-ci.com for a while

Fixes #3054

 - TCI Support
 - python 2.7
 - skip build-essential

Remove the call to `ls` that was used to determine the symlink
destination

Reasoning :

* `od` resolves symlink itself due to the use of `fopen`
* Prevent the behaviour of `od` which will hang if the filename is
  empty (i.e. `/sbin/init` missing) as it will be waiting for `stdin`
  compared to quitting with error if the file just doesn't exist

Fixes #3006

Incorporates old Contributing.md with more thorough details on how to contribute, create bug reports, set up the dev environment, and creating PR's itself.

[Docs] added WSL troubleshooting with solution to (6) Could not resolve host: raw.githubusercontent.com

Fixes #2958.

 - xenial can't build node 18
 - bionic can't build node 0.6 or 18

Fixes #2926