JOSS docs updates

[odunbar]

Purpose

Addresses #294

Content

Checked off from list in #294. The changes amount to the following.

• adds preferred installation via add CalibrateEmulateSample
• removes instructions to build pycall as this is now down within instantiation
• adds links to relevant EKP docs/examples for julia-free forward models
• adds detail to contribution sections for emulators (e.g. types), along with link in how-to-contribute pages
• adds diplomatic sentence to encourage users to try different emulators to explore tradeoffs.
• adds sentences to describe why one might want noise_learn = true for GP
• adds more clarifications to some of the RF optimizer options
• adds more detail into the RF kernel selection to avoid huge numbers of hyperparameters
• updates language in sample.md from the python-ic description,
• Add detail about Chains
• clears up all noted typos in issue
• adds the GaussianProcess() docstring to the API

updated docs here

---

• [x] I have read and checked the items on the review checklist.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.26%. Comparing base (acf1051) to head (813f4b2). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #296 +/- ## ========================================== + Coverage 88.17% 88.26% +0.08% ========================================== Files 8 8 Lines 1184 1184 ========================================== + Hits 1044 1045 +1 + Misses 140 139 -1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[odunbar]

deferring review to the JOSS referees