doc: include conda install command in installation guide

[beckermr]

Added conda installation instructions for jax-galsim.

[codspeed-hq]

Merging this PR will degrade performance by 39.17%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 2 regressed benchmarks
✅ 34 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	test_benchmarks_lanczos_interp[kval-conserve_dc-run]	43.4 µs	63.9 µs	-32.15%
❌	WallTime	test_benchmark_moffat_init[run]	57.4 µs	94.3 µs	-39.17%

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_{Comparing beckermr-patch-2 (1f47c3c) with main (d83c941)}

[ismael-mendoza]

Thanks @beckermr! Does the conda package get automatically updated everytime we make a new release in pypi?

[beckermr]

yes it will, but at a slower timescale