Improve documentation to include JNA configuration capabilities

Hi all,

testcontainers appears to be using JNA to perform its magic. By default, JNA writes to /tmp/jna folder and tries to execute something from there.

On some environments, /tmp folder is mounted with noexec flag, which makes the whole process fail.

Could you please add a documentation section where you specify your usage of JNA (maybe it's coming from docker-java?) and adding a note that properties jna.tmpdir and java.io.tmpdir can be used to override the default value?

A sample error that might occur during build with wrong configuration is:

ERROR o.t.d.EnvironmentAndSystemPropertyClientProviderStrategy.test - ping failed with configuration Environment variables, system properties and defaults. Resolved: 
[08:35:13][Step 2/5]     dockerHost=unix:///var/run/docker.sock
[08:35:13][Step 2/5]     apiVersion='{UNKNOWN_VERSION}'
[08:35:13][Step 2/5]     registryUrl='https://index.docker.io/v1/'
[08:35:13][Step 2/5]     registryUsername='xxx'
[08:35:13][Step 2/5]     registryPassword='null'
[08:35:13][Step 2/5]     registryEmail='null'
[08:35:13][Step 2/5]     dockerConfig='DefaultDockerClientConfig[dockerHost=unix:///var/run/docker.sock,registryUsername=xxx,registryPassword=<null>,registryEmail=<null>,registryUrl=https://index.docker.io/v1/,dockerConfigPath=/home/xxx/.docker,sslConfig=<null>,apiVersion={UNKNOWN_VERSION},dockerConfig=<null>]'
[08:35:13][Step 2/5]  due to java.lang.RuntimeException: java.lang.UnsatisfiedLinkError: /tmp/jna-100295547/jna9104525941980512569.tmp: /tmp/jna-100295547/jna9104525941980512569.tmp: failed to map segment from shared object: Operation not permitted
[08:35:13][Step 2/5] 	at org.rnorth.ducttape.timeouts.Timeouts.callFuture(Timeouts.java:68)

And I understand it is not directly your issue, but having a documentation section about it would help others in the future

Thanks and cheers